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git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull overflow updates from Kees Cook:
"This adds the new overflow checking helpers and adds them to the
2-factor argument allocators. And this adds the saturating size
helpers and does a treewide replacement for the struct_size() usage.
Additionally this adds the overflow testing modules to make sure
everything works.
I'm still working on the treewide replacements for allocators with
"simple" multiplied arguments:
*alloc(a * b, ...) -> *alloc_array(a, b, ...)
and
*zalloc(a * b, ...) -> *calloc(a, b, ...)
as well as the more complex cases, but that's separable from this
portion of the series. I expect to have the rest sent before -rc1
closes; there are a lot of messy cases to clean up.
Summary:
- Introduce arithmetic overflow test helper functions (Rasmus)
- Use overflow helpers in 2-factor allocators (Kees, Rasmus)
- Introduce overflow test module (Rasmus, Kees)
- Introduce saturating size helper functions (Matthew, Kees)
- Treewide use of struct_size() for allocators (Kees)"
* tag 'overflow-v4.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
treewide: Use struct_size() for devm_kmalloc() and friends
treewide: Use struct_size() for vmalloc()-family
treewide: Use struct_size() for kmalloc()-family
device: Use overflow helpers for devm_kmalloc()
mm: Use overflow helpers in kvmalloc()
mm: Use overflow helpers in kmalloc_array*()
test_overflow: Add memory allocation overflow tests
overflow.h: Add allocation size calculation helpers
test_overflow: Report test failures
test_overflow: macrofy some more, do more tests for free
lib: add runtime test of check_*_overflow functions
compiler.h: enable builtin overflow checkers and add fallback code
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One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:
struct foo {
int stuff;
void *entry[];
};
instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:
instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
This patch makes the changes for kmalloc()-family (and kvmalloc()-family)
uses. It was done via automatic conversion with manual review for the
"CHECKME" non-standard cases noted below, using the following Coccinelle
script:
// pkey_cache = kmalloc(sizeof *pkey_cache + tprops->pkey_tbl_len *
// sizeof *pkey_cache->table, GFP_KERNEL);
@@
identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc";
expression GFP;
identifier VAR, ELEMENT;
expression COUNT;
@@
- alloc(sizeof(*VAR) + COUNT * sizeof(*VAR->ELEMENT), GFP)
+ alloc(struct_size(VAR, ELEMENT, COUNT), GFP)
// mr = kzalloc(sizeof(*mr) + m * sizeof(mr->map[0]), GFP_KERNEL);
@@
identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc";
expression GFP;
identifier VAR, ELEMENT;
expression COUNT;
@@
- alloc(sizeof(*VAR) + COUNT * sizeof(VAR->ELEMENT[0]), GFP)
+ alloc(struct_size(VAR, ELEMENT, COUNT), GFP)
// Same pattern, but can't trivially locate the trailing element name,
// or variable name.
@@
identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc";
expression GFP;
expression SOMETHING, COUNT, ELEMENT;
@@
- alloc(sizeof(SOMETHING) + COUNT * sizeof(ELEMENT), GFP)
+ alloc(CHECKME_struct_size(&SOMETHING, ELEMENT, COUNT), GFP)
Signed-off-by: Kees Cook <keescook@chromium.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
Pull cgroup updates from Tejun Heo:
- For cpustat, cgroup has a percpu hierarchical stat mechanism which
propagates up the hierarchy lazily.
This contains commits to factor out and generalize the mechanism so
that it can be used for other cgroup stats too.
The original intention was to update memcg stats to use it but memcg
went for a different approach, so still the only user is cpustat. The
factoring out and generalization still make sense and it's likely
that this can be used for other purposes in the future.
- cgroup uses kernfs_notify() (which uses fsnotify()) to inform user
space of certain events. A rate limiting mechanism is added.
- Other misc changes.
* 'for-4.18' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup: css_set_lock should nest inside tasklist_lock
rdmacg: Convert to use match_string() helper
cgroup: Make cgroup_rstat_updated() ready for root cgroup usage
cgroup: Add memory barriers to plug cgroup_rstat_updated() race window
cgroup: Add cgroup_subsys->css_rstat_flush()
cgroup: Replace cgroup_rstat_mutex with a spinlock
cgroup: Factor out and expose cgroup_rstat_*() interface functions
cgroup: Reorganize kernel/cgroup/rstat.c
cgroup: Distinguish base resource stat implementation from rstat
cgroup: Rename stat to rstat
cgroup: Rename kernel/cgroup/stat.c to kernel/cgroup/rstat.c
cgroup: Limit event generation frequency
cgroup: Explicitly remove core interface files
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cgroup_enable_task_cg_lists() incorrectly nests non-irq-safe
tasklist_lock inside irq-safe css_set_lock triggering the following
lockdep warning.
WARNING: possible irq lock inversion dependency detected
4.17.0-rc1-00027-gb37d049 #6 Not tainted
--------------------------------------------------------
systemd/1 just changed the state of lock:
00000000fe57773b (css_set_lock){..-.}, at: cgroup_free+0xf2/0x12a
but this lock took another, SOFTIRQ-unsafe lock in the past:
(tasklist_lock){.+.+}
and interrupts could create inverse lock ordering between them.
other info that might help us debug this:
Possible interrupt unsafe locking scenario:
CPU0 CPU1
---- ----
lock(tasklist_lock);
local_irq_disable();
lock(css_set_lock);
lock(tasklist_lock);
<Interrupt>
lock(css_set_lock);
*** DEADLOCK ***
The condition is highly unlikely to actually happen especially given
that the path is executed only once per boot.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Boqun Feng <boqun.feng@gmail.com>
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Variants of proc_create{,_data} that directly take a seq_file show
callback and drastically reduces the boilerplate code in the callers.
All trivial callers converted over.
Signed-off-by: Christoph Hellwig <hch@lst.de>
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This patch adds cgroup_subsys->css_rstat_flush(). If a subsystem has
this callback, its csses are linked on cgrp->css_rstat_list and rstat
will call the function whenever the associated cgroup is flushed.
Flush is also performed when such csses are released so that residual
counts aren't lost.
Combined with the rstat API previous patches factored out, this allows
controllers to plug into rstat to manage their statistics in a
scalable way.
Signed-off-by: Tejun Heo <tj@kernel.org>
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Base resource stat accounts universial (not specific to any
controller) resource consumptions on top of rstat. Currently, its
implementation is intermixed with rstat implementation making the code
confusing to follow.
This patch clarifies the distintion by doing the followings.
* Encapsulate base resource stat counters, currently only cputime, in
struct cgroup_base_stat.
* Move prev_cputime into struct cgroup and initialize it with cgroup.
* Rename the related functions so that they start with cgroup_base_stat.
* Prefix the related variables and field names with b.
This patch doesn't make any functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
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stat is too generic a name and ends up causing subtle confusions.
It'll be made generic so that controllers can plug into it, which will
make the problem worse. Let's rename it to something more specific -
cgroup_rstat for cgroup recursive stat.
This patch does the following renames. No other changes.
* cpu_stat -> rstat_cpu
* stat -> rstat
* ?cstat -> ?rstatc
Note that the renames are selective. The unrenamed are the ones which
implement basic resource statistics on top of rstat. This will be
further cleaned up in the following patches.
Signed-off-by: Tejun Heo <tj@kernel.org>
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".events" files generate file modified event to notify userland of
possible new events. Some of the events can be quite bursty
(e.g. memory high event) and generating notification each time is
costly and pointless.
This patch implements a event rate limit mechanism. If a new
notification is requested before 10ms has passed since the previous
notification, the new notification is delayed till then.
As this only delays from the second notification on in a given close
cluster of notifications, userland reactions to notifications
shouldn't be delayed at all in most cases while avoiding notification
storms.
Signed-off-by: Tejun Heo <tj@kernel.org>
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The "cgroup." core interface files bypass the usual interface removal
path and get removed recursively along with the cgroup itself. While
this works now, the subtle discrepancy gets in the way of implementing
common mechanisms.
This patch updates cgroup core interface file handling so that it's
consistent with controller interface files. When added, the css is
marked CSS_VISIBLE and they're explicitly removed before the cgroup is
destroyed.
This doesn't cause user-visible behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
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Pull workqueue updates from Tejun Heo:
"rcu_work addition and a couple trivial changes"
* 'for-4.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
workqueue: remove the comment about the old manager_arb mutex
workqueue: fix the comments of nr_idle
fs/aio: Use rcu_work instead of explicit rcu and work item
cgroup: Use rcu_work instead of explicit rcu and work item
RCU, workqueue: Implement rcu_work
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Workqueue now has rcu_work. Use it instead of open-coding rcu -> work
item bouncing.
Signed-off-by: Tejun Heo <tj@kernel.org>
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A domain cgroup isn't allowed to be turned threaded if its subtree is
populated or domain controllers are enabled. cgroup_enable_threaded()
depended on cgroup_can_be_thread_root() test to enforce this rule. A
parent which has populated domain descendants or have domain
controllers enabled can't become a thread root, so the above rules are
enforced automatically.
However, for the root cgroup which can host mixed domain and threaded
children, cgroup_can_be_thread_root() doesn't check any of those
conditions and thus first level cgroups ends up escaping those rules.
This patch fixes the bug by adding explicit checks for those rules in
cgroup_enable_threaded().
Reported-by: Michael Kerrisk (man-pages) <mtk.manpages@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 8cfd8147df67 ("cgroup: implement cgroup v2 thread support")
Cc: stable@vger.kernel.org # v4.14+
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e7fd37ba1217 ("cgroup: avoid copying strings longer than the buffers")
converted possibly unsafe strncpy() usages in cgroup to strscpy().
However, although the callsites are completely fine with truncated
copied, because strscpy() is marked __must_check, it led to the
following warnings.
kernel/cgroup/cgroup.c: In function ‘cgroup_file_name’:
kernel/cgroup/cgroup.c:1400:10: warning: ignoring return value of ‘strscpy’, declared with attribute warn_unused_result [-Wunused-result]
strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
^
To avoid the warnings, 50034ed49645 ("cgroup: use strlcpy() instead of
strscpy() to avoid spurious warning") switched them to strlcpy().
strlcpy() is worse than strlcpy() because it unconditionally runs
strlen() on the source string, and the only reason we switched to
strlcpy() here was because it was lacking __must_check, which doesn't
reflect any material differences between the two function. It's just
that someone added __must_check to strscpy() and not to strlcpy().
These basic string copy operations are used in variety of ways, and
one of not-so-uncommon use cases is safely handling truncated copies,
where the caller naturally doesn't care about the return value. The
__must_check doesn't match the actual use cases and forces users to
opt for inferior variants which lack __must_check by happenstance or
spread ugly (void) casts.
Remove __must_check from strscpy() and restore strscpy() usages in
cgroup.
Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
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Make cgroup.threads file delegatable.
The behavior of cgroup.threads should follow the behavior of cgroup.procs.
Signed-off-by: Roman Gushchin <guro@fb.com>
Discovered-by: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
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While teaching css_task_iter to handle skipping over tasks which
aren't group leaders, bc2fb7ed089f ("cgroup: add @flags to
css_task_iter_start() and implement CSS_TASK_ITER_PROCS") introduced a
silly bug.
CSS_TASK_ITER_PROCS is implemented by repeating
css_task_iter_advance() while the advanced cursor is pointing to a
non-leader thread. However, the cursor variable, @l, wasn't updated
when the iteration has to advance to the next css_set and the
following repetition would operate on the terminal @l from the
previous iteration which isn't pointing to a valid task leading to
oopses like the following or infinite looping.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000254
IP: __task_pid_nr_ns+0xc7/0xf0
PGD 0 P4D 0
Oops: 0000 [#1] SMP
...
CPU: 2 PID: 1 Comm: systemd Not tainted 4.14.4-200.fc26.x86_64 #1
Hardware name: System manufacturer System Product Name/PRIME B350M-A, BIOS 3203 11/09/2017
task: ffff88c4baee8000 task.stack: ffff96d5c3158000
RIP: 0010:__task_pid_nr_ns+0xc7/0xf0
RSP: 0018:ffff96d5c315bd50 EFLAGS: 00010206
RAX: 0000000000000000 RBX: ffff88c4b68c6000 RCX: 0000000000000250
RDX: ffffffffa5e47960 RSI: 0000000000000000 RDI: ffff88c490f6ab00
RBP: ffff96d5c315bd50 R08: 0000000000001000 R09: 0000000000000005
R10: ffff88c4be006b80 R11: ffff88c42f1b8004 R12: ffff96d5c315bf18
R13: ffff88c42d7dd200 R14: ffff88c490f6a510 R15: ffff88c4b68c6000
FS: 00007f9446f8ea00(0000) GS:ffff88c4be680000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000254 CR3: 00000007f956f000 CR4: 00000000003406e0
Call Trace:
cgroup_procs_show+0x19/0x30
cgroup_seqfile_show+0x4c/0xb0
kernfs_seq_show+0x21/0x30
seq_read+0x2ec/0x3f0
kernfs_fop_read+0x134/0x180
__vfs_read+0x37/0x160
? security_file_permission+0x9b/0xc0
vfs_read+0x8e/0x130
SyS_read+0x55/0xc0
entry_SYSCALL_64_fastpath+0x1a/0xa5
RIP: 0033:0x7f94455f942d
RSP: 002b:00007ffe81ba2d00 EFLAGS: 00000293 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00005574e2233f00 RCX: 00007f94455f942d
RDX: 0000000000001000 RSI: 00005574e2321a90 RDI: 000000000000002b
RBP: 0000000000000000 R08: 00005574e2321a90 R09: 00005574e231de60
R10: 00007f94458c8b38 R11: 0000000000000293 R12: 00007f94458c8ae0
R13: 00007ffe81ba3800 R14: 0000000000000000 R15: 00005574e2116560
Code: 04 74 0e 89 f6 48 8d 04 76 48 8d 04 c5 f0 05 00 00 48 8b bf b8 05 00 00 48 01 c7 31 c0 48 8b 0f 48 85 c9 74 18 8b b2 30 08 00 00 <3b> 71 04 77 0d 48 c1 e6 05 48 01 f1 48 3b 51 38 74 09 5d c3 8b
RIP: __task_pid_nr_ns+0xc7/0xf0 RSP: ffff96d5c315bd50
Fix it by moving the initialization of the cursor below the repeat
label. While at it, rename it to @next for readability.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: bc2fb7ed089f ("cgroup: add @flags to css_task_iter_start() and implement CSS_TASK_ITER_PROCS")
Cc: stable@vger.kernel.org # v4.14+
Reported-by: Laura Abbott <labbott@redhat.com>
Reported-by: Bronek Kozicki <brok@incorrekt.com>
Reported-by: George Amanakis <gamanakis@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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As long as cft->name is guaranteed to be NUL-terminated, using strlcpy() would
work just as well and avoid that warning, so the change below could be folded
into that commit.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
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cgroup root name and file name have max length limit, we should
avoid copying longer name than that to the name.
tj: minor update to $SUBJ.
Signed-off-by: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
Pull cgroup updates from Tejun Heo:
"Cgroup2 cpu controller support is finally merged.
- Basic cpu statistics support to allow monitoring by default without
the CPU controller enabled.
- cgroup2 cpu controller support.
- /sys/kernel/cgroup files to help dealing with new / optional
features"
* 'for-4.15' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup: export list of cgroups v2 features using sysfs
cgroup: export list of delegatable control files using sysfs
cgroup: mark @cgrp __maybe_unused in cpu_stat_show()
MAINTAINERS: relocate cpuset.c
cgroup, sched: Move basic cpu stats from cgroup.stat to cpu.stat
sched: Implement interface for cgroup unified hierarchy
sched: Misc preps for cgroup unified hierarchy interface
sched/cputime: Add dummy cputime_adjust() implementation for CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
cgroup: statically initialize init_css_set->dfl_cgrp
cgroup: Implement cgroup2 basic CPU usage accounting
cpuacct: Introduce cgroup_account_cputime[_field]()
sched/cputime: Expose cputime_adjust()
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The active development of cgroups v2 sometimes leads to a creation
of interfaces, which are not turned on by default (to provide
backward compatibility). It's handy to know from userspace, which
cgroup v2 features are supported without calculating it based
on the kernel version. So, let's export the list of such features
using /sys/kernel/cgroup/features pseudo-file.
The list is hardcoded and has to be extended when new functionality
is added. Each feature is printed on a new line.
Example:
$ cat /sys/kernel/cgroup/features
nsdelegate
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
Signed-off-by: Tejun Heo <tj@kernel.org>
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Delegatable cgroup v2 control files may require special handling
(e.g. chowning), and the exact list of such files varies between
kernel versions (and likely to be extended in the future).
To guarantee correctness of this list and simplify the life
of userspace (systemd, first of all), let's export the list
via /sys/kernel/cgroup/delegate pseudo-file.
Format is siple: each control file name is printed on a new line.
Example:
$ cat /sys/kernel/cgroup/delegate
cgroup.procs
cgroup.subtree_control
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
Signed-off-by: Tejun Heo <tj@kernel.org>
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The local variable @cgrp isn't used if !CONFIG_CGROUP_SCHED. Mark the
variable with __maybe_unused to avoid a compile warning.
Reported-by: "kbuild-all@01.org" <kbuild-all@01.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
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The basic cpu stat is currently shown with "cpu." prefix in
cgroup.stat, and the same information is duplicated in cpu.stat when
cpu controller is enabled. This is ugly and not very scalable as we
want to expand the coverage of stat information which is always
available.
This patch makes cgroup core always create "cpu.stat" file and show
the basic cpu stat there and calls the cpu controller to show the
extra stats when enabled. This ensures that the same information
isn't presented in multiple places and makes future expansion of basic
stats easier.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Just simple overlapping changes.
Signed-off-by: David S. Miller <davem@davemloft.net>
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introduce BPF_PROG_QUERY command to retrieve a set of either
attached programs to given cgroup or a set of effective programs
that will execute for events within a cgroup
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
for cgroup bits
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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introduce BPF_F_ALLOW_MULTI flag that can be used to attach multiple
bpf programs to a cgroup.
The difference between three possible flags for BPF_PROG_ATTACH command:
- NONE(default): No further bpf programs allowed in the subtree.
- BPF_F_ALLOW_OVERRIDE: If a sub-cgroup installs some bpf program,
the program in this cgroup yields to sub-cgroup program.
- BPF_F_ALLOW_MULTI: If a sub-cgroup installs some bpf program,
that cgroup program gets run in addition to the program in this cgroup.
NONE and BPF_F_ALLOW_OVERRIDE existed before. This patch doesn't
change their behavior. It only clarifies the semantics in relation
to new flag.
Only one program is allowed to be attached to a cgroup with
NONE or BPF_F_ALLOW_OVERRIDE flag.
Multiple programs are allowed to be attached to a cgroup with
BPF_F_ALLOW_MULTI flag. They are executed in FIFO order
(those that were attached first, run first)
The programs of sub-cgroup are executed first, then programs of
this cgroup and then programs of parent cgroup.
All eligible programs are executed regardless of return code from
earlier programs.
To allow efficient execution of multiple programs attached to a cgroup
and to avoid penalizing cgroups without any programs attached
introduce 'struct bpf_prog_array' which is RCU protected array
of pointers to bpf programs.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
for cgroup bits
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Like other csets, init_css_set's dfl_cgrp is initialized when the cset
gets linked. init_css_set gets linked in cgroup_init(). This has
been fine till now but the recently added basic CPU usage accounting
may end up accessing dfl_cgrp of init before cgroup_init() leading to
the following oops.
SELinux: Initializing.
BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0
IP: account_system_index_time+0x60/0x90
PGD 0 P4D 0
Oops: 0000 [#1] SMP
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc2-00003-g041cd64 #10
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
+1.9.3-20161025_171302-gandalf 04/01/2014
task: ffffffff81e10480 task.stack: ffffffff81e00000
RIP: 0010:account_system_index_time+0x60/0x90
RSP: 0000:ffff880011e03cb8 EFLAGS: 00010002
RAX: ffffffff81ef8800 RBX: ffffffff81e10480 RCX: 0000000000000003
RDX: 0000000000000000 RSI: 00000000000f4240 RDI: 0000000000000000
RBP: ffff880011e03cc0 R08: 0000000000010000 R09: 0000000000000000
R10: 0000000000000020 R11: 0000003b9aca0000 R12: 000000000001c100
R13: 0000000000000000 R14: ffffffff81e10480 R15: ffffffff81e03cd8
FS: 0000000000000000(0000) GS:ffff880011e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000000b0 CR3: 0000000001e09000 CR4: 00000000000006b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
account_system_time+0x45/0x60
account_process_tick+0x5a/0x140
update_process_times+0x22/0x60
tick_periodic+0x2b/0x90
tick_handle_periodic+0x25/0x70
timer_interrupt+0x15/0x20
__handle_irq_event_percpu+0x7e/0x1b0
handle_irq_event_percpu+0x23/0x60
handle_irq_event+0x42/0x70
handle_level_irq+0x83/0x100
handle_irq+0x6f/0x110
do_IRQ+0x46/0xd0
common_interrupt+0x9d/0x9d
Fix it by statically initializing init_css_set.dfl_cgrp so that init's
default cgroup is accessible from the get-go.
Fixes: 041cd640b2f3 ("cgroup: Implement cgroup2 basic CPU usage accounting")
Reported-by: “kbuild-all@01.org” <kbuild-all@01.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
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In cgroup1, while cpuacct isn't actually controlling any resources, it
is a separate controller due to combination of two factors -
1. enabling cpu controller has significant side effects, and 2. we
have to pick one of the hierarchies to account CPU usages on. cpuacct
controller is effectively used to designate a hierarchy to track CPU
usages on.
cgroup2's unified hierarchy removes the second reason and we can
account basic CPU usages by default. While we can use cpuacct for
this purpose, both its interface and implementation leave a lot to be
desired - it collects and exposes two sources of truth which don't
agree with each other and some of the exposed statistics don't make
much sense. Also, it propagates all the way up the hierarchy on each
accounting event which is unnecessary.
This patch adds basic resource accounting mechanism to cgroup2's
unified hierarchy and accounts CPU usages using it.
* All accountings are done per-cpu and don't propagate immediately.
It just bumps the per-cgroup per-cpu counters and links to the
parent's updated list if not already on it.
* On a read, the per-cpu counters are collected into the global ones
and then propagated upwards. Only the per-cpu counters which have
changed since the last read are propagated.
* CPU usage stats are collected and shown in "cgroup.stat" with "cpu."
prefix. Total usage is collected from scheduling events. User/sys
breakdown is sourced from tick sampling and adjusted to the usage
using cputime_adjust().
This keeps the accounting side hot path O(1) and per-cpu and the read
side O(nr_updated_since_last_read).
v2: Minor changes and documentation updates as suggested by Waiman and
Roman.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Roman Gushchin <guro@fb.com>
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The cgroup_taskset structure within the larger cgroup_mgctx structure
is supposed to be used once and then discarded. That is not really the
case in the hotplug code path:
cpuset_hotplug_workfn()
- cgroup_transfer_tasks()
- cgroup_migrate()
- cgroup_migrate_add_task()
- cgroup_migrate_execute()
In this case, the cgroup_migrate() function is called multiple time
with the same cgroup_mgctx structure to transfer the tasks from
one cgroup to another one-by-one. The second time cgroup_migrate()
is called, the cgroup_taskset will be in an incorrect state and so
may cause the system to panic. For example,
[ 150.888410] Faulting instruction address: 0xc0000000001db648
[ 150.888414] Oops: Kernel access of bad area, sig: 11 [#1]
[ 150.888417] SMP NR_CPUS=2048
[ 150.888417] NUMA
[ 150.888419] pSeries
:
[ 150.888545] NIP [c0000000001db648] cpuset_can_attach+0x58/0x1b0
[ 150.888548] LR [c0000000001db638] cpuset_can_attach+0x48/0x1b0
[ 150.888551] Call Trace:
[ 150.888554] [c0000005f65cb940] [c0000000001db638] cpuset_can_attach+0x48/0x1b 0 (unreliable)
[ 150.888559] [c0000005f65cb9a0] [c0000000001cff04] cgroup_migrate_execute+0xc4/0x4b0
[ 150.888563] [c0000005f65cba20] [c0000000001d7d14] cgroup_transfer_tasks+0x1d4/0x370
[ 150.888568] [c0000005f65cbb70] [c0000000001ddcb0] cpuset_hotplug_workfn+0x710/0x8f0
[ 150.888572] [c0000005f65cbc80] [c00000000012032c] process_one_work+0x1ac/0x4d0
[ 150.888576] [c0000005f65cbd20] [c0000000001206f8] worker_thread+0xa8/0x5b0
[ 150.888580] [c0000005f65cbdc0] [c0000000001293f8] kthread+0x168/0x1b0
[ 150.888584] [c0000005f65cbe30] [c00000000000b368] ret_from_kernel_thread+0x5c/0x74
To allow reuse of the cgroup_mgctx structure, some fields in that
structure are now re-initialized at the end of cgroup_migrate_execute()
function call so that the structure can be reused again in a later
iteration without causing problem.
This bug was introduced in the commit e595cd706982 ("group: track
migration context in cgroup_mgctx") in 4.11. This commit moves the
cgroup_taskset initialization out of cgroup_migrate(). The commit
10467270fb3 ("cgroup: don't call migration methods if there are no
tasks to migrate") helped, but did not completely resolve the problem.
Fixes: e595cd706982bff0211e6fafe5a108421e747fbc ("group: track migration context in cgroup_mgctx")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v4.11+
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Pull block layer updates from Jens Axboe:
"This is the first pull request for 4.14, containing most of the code
changes. It's a quiet series this round, which I think we needed after
the churn of the last few series. This contains:
- Fix for a registration race in loop, from Anton Volkov.
- Overflow complaint fix from Arnd for DAC960.
- Series of drbd changes from the usual suspects.
- Conversion of the stec/skd driver to blk-mq. From Bart.
- A few BFQ improvements/fixes from Paolo.
- CFQ improvement from Ritesh, allowing idling for group idle.
- A few fixes found by Dan's smatch, courtesy of Dan.
- A warning fixup for a race between changing the IO scheduler and
device remova. From David Jeffery.
- A few nbd fixes from Josef.
- Support for cgroup info in blktrace, from Shaohua.
- Also from Shaohua, new features in the null_blk driver to allow it
to actually hold data, among other things.
- Various corner cases and error handling fixes from Weiping Zhang.
- Improvements to the IO stats tracking for blk-mq from me. Can
drastically improve performance for fast devices and/or big
machines.
- Series from Christoph removing bi_bdev as being needed for IO
submission, in preparation for nvme multipathing code.
- Series from Bart, including various cleanups and fixes for switch
fall through case complaints"
* 'for-4.14/block' of git://git.kernel.dk/linux-block: (162 commits)
kernfs: checking for IS_ERR() instead of NULL
drbd: remove BIOSET_NEED_RESCUER flag from drbd_{md_,}io_bio_set
drbd: Fix allyesconfig build, fix recent commit
drbd: switch from kmalloc() to kmalloc_array()
drbd: abort drbd_start_resync if there is no connection
drbd: move global variables to drbd namespace and make some static
drbd: rename "usermode_helper" to "drbd_usermode_helper"
drbd: fix race between handshake and admin disconnect/down
drbd: fix potential deadlock when trying to detach during handshake
drbd: A single dot should be put into a sequence.
drbd: fix rmmod cleanup, remove _all_ debugfs entries
drbd: Use setup_timer() instead of init_timer() to simplify the code.
drbd: fix potential get_ldev/put_ldev refcount imbalance during attach
drbd: new disk-option disable-write-same
drbd: Fix resource role for newly created resources in events2
drbd: mark symbols static where possible
drbd: Send P_NEG_ACK upon write error in protocol != C
drbd: add explicit plugging when submitting batches
drbd: change list_for_each_safe to while(list_first_entry_or_null)
drbd: introduce drbd_recv_header_maybe_unplug
...
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git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
Pull cgroup updates from Tejun Heo:
"Several notable changes this cycle:
- Thread mode was merged. This will be used for cgroup2 support for
CPU and possibly other controllers. Unfortunately, CPU controller
cgroup2 support didn't make this pull request but most contentions
have been resolved and the support is likely to be merged before
the next merge window.
- cgroup.stat now shows the number of descendant cgroups.
- cpuset now can enable the easier-to-configure v2 behavior on v1
hierarchy"
* 'for-4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: (21 commits)
cpuset: Allow v2 behavior in v1 cgroup
cgroup: Add mount flag to enable cpuset to use v2 behavior in v1 cgroup
cgroup: remove unneeded checks
cgroup: misc changes
cgroup: short-circuit cset_cgroup_from_root() on the default hierarchy
cgroup: re-use the parent pointer in cgroup_destroy_locked()
cgroup: add cgroup.stat interface with basic hierarchy stats
cgroup: implement hierarchy limits
cgroup: keep track of number of descent cgroups
cgroup: add comment to cgroup_enable_threaded()
cgroup: remove unnecessary empty check when enabling threaded mode
cgroup: update debug controller to print out thread mode information
cgroup: implement cgroup v2 thread support
cgroup: implement CSS_TASK_ITER_THREADED
cgroup: introduce cgroup->dom_cgrp and threaded css_set handling
cgroup: add @flags to css_task_iter_start() and implement CSS_TASK_ITER_PROCS
cgroup: reorganize cgroup.procs / task write path
cgroup: replace css_set walking populated test with testing cgrp->nr_populated_csets
cgroup: distinguish local and children populated states
cgroup: remove now unused list_head @pending in cgroup_apply_cftypes()
...
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Commit fa06235b8eb0 ("cgroup: reset css on destruction") caused
css_reset callback to be called from the offlining path. Although it
solves the problem mentioned in the commit description ("For instance,
memory cgroup needs to reset memory.low, otherwise pages charged to a
dead cgroup might never get reclaimed."), generally speaking, it's not
correct.
An offline cgroup can still be a resource domain, and we shouldn't grant
it more resources than it had before deletion.
For instance, if an offline memory cgroup has dirty pages, we should
still imply i/o limits during writeback.
The css_reset callback is designed to return the cgroup state into the
original state, that means reset all limits and counters. It's
spomething different from the offlining, and we shouldn't use it from
the offlining path. Instead, we should adjust necessary settings from
the per-controller css_offline callbacks (e.g. reset memory.low).
Link: http://lkml.kernel.org/r/20170727130428.28856-2-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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"descendants" and "depth" are declared as int, so they can't be larger
than INT_MAX. Static checkers complain and it's slightly confusing for
humans as well so let's just remove these conditions.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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Misc trivial changes to prepare for future changes. No functional
difference.
* Expose cgroup_get(), cgroup_tryget() and cgroup_parent().
* Implement task_dfl_cgroup() which dereferences css_set->dfl_cgrp.
* Rename cgroup_stats_show() to cgroup_stat_show() for consistency
with the file name.
Signed-off-by: Tejun Heo <tj@kernel.org>
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Each css_set directly points to the default cgroup it belongs to, so
there's no reason to walk the cgrp_links list on the default
hierarchy.
Signed-off-by: Tejun Heo <tj@kernel.org>
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As we already have a pointer to the parent cgroup in
cgroup_destroy_locked(), we don't need to calculate it again
to pass as an argument for cgroup1_check_for_release().
Signed-off-by: Roman Gushchin <guro@fb.com>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kernel-team@fb.com
Cc: linux-kernel@vger.kernel.org
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A cgroup can consume resources even after being deleted by a user.
For example, writing back dirty pages should be accounted and
limited, despite the corresponding cgroup might contain no processes
and being deleted by a user.
In the current implementation a cgroup can remain in such "dying" state
for an undefined amount of time. For instance, if a memory cgroup
contains a pge, mlocked by a process belonging to an other cgroup.
Although the lifecycle of a dying cgroup is out of user's control,
it's important to have some insight of what's going on under the hood.
In particular, it's handy to have a counter which will allow
to detect css leaks.
To solve this problem, add a cgroup.stat interface to
the base cgroup control files with the following metrics:
nr_descendants total number of visible descendant cgroups
nr_dying_descendants total number of dying descendant cgroups
Signed-off-by: Roman Gushchin <guro@fb.com>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kernel-team@fb.com
Cc: cgroups@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
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Creating cgroup hierearchies of unreasonable size can affect
overall system performance. A user might want to limit the
size of cgroup hierarchy. This is especially important if a user
is delegating some cgroup sub-tree.
To address this issue, introduce an ability to control
the size of cgroup hierarchy.
The cgroup.max.descendants control file allows to set the maximum
allowed number of descendant cgroups.
The cgroup.max.depth file controls the maximum depth of the cgroup
tree. Both are single value r/w files, with "max" default value.
The control files exist on each hierarchy level (including root).
When a new cgroup is created, we check the total descendants
and depth limits on each level, and if none of them are exceeded,
a new cgroup is created.
Only alive cgroups are counted, removed (dying) cgroups are
ignored.
Signed-off-by: Roman Gushchin <guro@fb.com>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kernel-team@fb.com
Cc: cgroups@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
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Keep track of the number of online and dying descent cgroups.
This data will be used later to add an ability to control cgroup
hierarchy (limit the depth and the number of descent cgroups)
and display hierarchy stats.
Signed-off-by: Roman Gushchin <guro@fb.com>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kernel-team@fb.com
Cc: cgroups@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
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By default we output cgroup id in blktrace. This adds an option to
display cgroup path. Since get cgroup path is a relativly heavy
operation, we don't enable it by default.
with the option enabled, blktrace will output something like this:
dd-1353 [007] d..2 293.015252: 8,0 /test/level D R 24 + 8 [dd]
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Now we have the facilities to implement exportfs operations. The idea is
cgroup can export the fhandle info to userspace, then userspace uses
fhandle to find the cgroup name. Another example is userspace can get
fhandle for a cgroup and BPF uses the fhandle to filter info for the
cgroup.
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Explain cgroup_enable_threaded() and note that the function can never
be called on the root cgroup.
Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Waiman Long <longman@redhat.com>
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cgroup_enable_threaded() checks that the cgroup doesn't have any tasks
or children and fails the operation if so. This test is unnecessary
because the first part is already checked by
cgroup_can_be_thread_root() and the latter is unnecessary. The latter
actually cause a behavioral oddity. Please consider the following
hierarchy. All cgroups are domains.
A
/ \
B C
\
D
If B is made threaded, C and D becomes invalid domains. Due to the no
children restriction, threaded mode can't be enabled on C. For C and
D, the only thing the user can do is removal.
There is no reason for this restriction. Remove it.
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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While refactoring, f7b2814bb9b6 ("cgroup: factor out
cgroup_{apply|finalize}_control() from
cgroup_subtree_control_write()") broke error return value from the
function. The return value from the last operation is always
overridden to zero. Fix it.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v4.6+
Signed-off-by: Tejun Heo <tj@kernel.org>
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Update debug controller so that it prints out debug info about thread
mode.
1) The relationship between proc_cset and threaded_csets are displayed.
2) The status of being a thread root or threaded cgroup is displayed.
This patch is extracted from Waiman's larger patch.
v2: - Removed [thread root] / [threaded] from debug.cgroup_css_links
file as the same information is available from cgroup.type.
Suggested by Waiman.
- Threaded marking is moved to the previous patch.
Patch-originally-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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This patch implements cgroup v2 thread support. The goal of the
thread mode is supporting hierarchical accounting and control at
thread granularity while staying inside the resource domain model
which allows coordination across different resource controllers and
handling of anonymous resource consumptions.
A cgroup is always created as a domain and can be made threaded by
writing to the "cgroup.type" file. When a cgroup becomes threaded, it
becomes a member of a threaded subtree which is anchored at the
closest ancestor which isn't threaded.
The threads of the processes which are in a threaded subtree can be
placed anywhere without being restricted by process granularity or
no-internal-process constraint. Note that the threads aren't allowed
to escape to a different threaded subtree. To be used inside a
threaded subtree, a controller should explicitly support threaded mode
and be able to handle internal competition in the way which is
appropriate for the resource.
The root of a threaded subtree, the nearest ancestor which isn't
threaded, is called the threaded domain and serves as the resource
domain for the whole subtree. This is the last cgroup where domain
controllers are operational and where all the domain-level resource
consumptions in the subtree are accounted. This allows threaded
controllers to operate at thread granularity when requested while
staying inside the scope of system-level resource distribution.
As the root cgroup is exempt from the no-internal-process constraint,
it can serve as both a threaded domain and a parent to normal cgroups,
so, unlike non-root cgroups, the root cgroup can have both domain and
threaded children.
Internally, in a threaded subtree, each css_set has its ->dom_cset
pointing to a matching css_set which belongs to the threaded domain.
This ensures that thread root level cgroup_subsys_state for all
threaded controllers are readily accessible for domain-level
operations.
This patch enables threaded mode for the pids and perf_events
controllers. Neither has to worry about domain-level resource
consumptions and it's enough to simply set the flag.
For more details on the interface and behavior of the thread mode,
please refer to the section 2-2-2 in Documentation/cgroup-v2.txt added
by this patch.
v5: - Dropped silly no-op ->dom_cgrp init from cgroup_create().
Spotted by Waiman.
- Documentation updated as suggested by Waiman.
- cgroup.type content slightly reformatted.
- Mark the debug controller threaded.
v4: - Updated to the general idea of marking specific cgroups
domain/threaded as suggested by PeterZ.
v3: - Dropped "join" and always make mixed children join the parent's
threaded subtree.
v2: - After discussions with Waiman, support for mixed thread mode is
added. This should address the issue that Peter pointed out
where any nesting should be avoided for thread subtrees while
coexisting with other domain cgroups.
- Enabling / disabling thread mode now piggy backs on the existing
control mask update mechanism.
- Bug fixes and cleanup.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
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cgroup v2 is in the process of growing thread granularity support.
Once thread mode is enabled, the root cgroup of the subtree serves as
the dom_cgrp to which the processes of the subtree conceptually belong
and domain-level resource consumptions not tied to any specific task
are charged. In the subtree, threads won't be subject to process
granularity or no-internal-task constraint and can be distributed
arbitrarily across the subtree.
This patch implements a new task iterator flag CSS_TASK_ITER_THREADED,
which, when used on a dom_cgrp, makes the iteration include the tasks
on all the associated threaded css_sets. "cgroup.procs" read path is
updated to use it so that reading the file on a proc_cgrp lists all
processes. This will also be used by controller implementations which
need to walk processes or tasks at the resource domain level.
Task iteration is implemented nested in css_set iteration. If
CSS_TASK_ITER_THREADED is specified, after walking tasks of each
!threaded css_set, all the associated threaded css_sets are visited
before moving onto the next !threaded css_set.
v2: ->cur_pcset renamed to ->cur_dcset. Updated for the new
enable-threaded-per-cgroup behavior.
Signed-off-by: Tejun Heo <tj@kernel.org>
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cgroup v2 is in the process of growing thread granularity support. A
threaded subtree is composed of a thread root and threaded cgroups
which are proper members of the subtree.
The root cgroup of the subtree serves as the domain cgroup to which
the processes (as opposed to threads / tasks) of the subtree
conceptually belong and domain-level resource consumptions not tied to
any specific task are charged. Inside the subtree, threads won't be
subject to process granularity or no-internal-task constraint and can
be distributed arbitrarily across the subtree.
This patch introduces cgroup->dom_cgrp along with threaded css_set
handling.
* cgroup->dom_cgrp points to self for normal and thread roots. For
proper thread subtree members, points to the dom_cgrp (the thread
root).
* css_set->dom_cset points to self if for normal and thread roots. If
threaded, points to the css_set which belongs to the cgrp->dom_cgrp.
The dom_cgrp serves as the resource domain and keeps the matching
csses available. The dom_cset holds those csses and makes them
easily accessible.
* All threaded csets are linked on their dom_csets to enable iteration
of all threaded tasks.
* cgroup->nr_threaded_children keeps track of the number of threaded
children.
This patch adds the above but doesn't actually use them yet. The
following patches will build on top.
v4: ->nr_threaded_children added.
v3: ->proc_cgrp/cset renamed to ->dom_cgrp/cset. Updated for the new
enable-threaded-per-cgroup behavior.
v2: Added cgroup_is_threaded() helper.
Signed-off-by: Tejun Heo <tj@kernel.org>
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css_task_iter currently always walks all tasks. With the scheduled
cgroup v2 thread support, the iterator would need to handle multiple
types of iteration. As a preparation, add @flags to
css_task_iter_start() and implement CSS_TASK_ITER_PROCS. If the flag
is not specified, it walks all tasks as before. When asserted, the
iterator only walks the group leaders.
For now, the only user of the flag is cgroup v2 "cgroup.procs" file
which no longer needs to skip non-leader tasks in cgroup_procs_next().
Note that cgroup v1 "cgroup.procs" can't use the group leader walk as
v1 "cgroup.procs" doesn't mean "list all thread group leaders in the
cgroup" but "list all thread group id's with any threads in the
cgroup".
While at it, update cgroup_procs_show() to use task_pid_vnr() instead
of task_tgid_vnr(). As the iteration guarantees that the function
only sees group leaders, this doesn't change the output and will allow
sharing the function for thread iteration.
Signed-off-by: Tejun Heo <tj@kernel.org>
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Currently, writes "cgroup.procs" and "cgroup.tasks" files are all
handled by __cgroup_procs_write() on both v1 and v2. This patch
reoragnizes the write path so that there are common helper functions
that different write paths use.
While this somewhat increases LOC, the different paths are no longer
intertwined and each path has more flexibility to implement different
behaviors which will be necessary for the planned v2 thread support.
v3: - Restructured so that cgroup_procs_write_permission() takes
@src_cgrp and @dst_cgrp.
v2: - Rolled in Waiman's task reference count fix.
- Updated on top of nsdelegate changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@redhat.com>
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