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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/spdx
Pull SPDX updates from Greg KH:
"Here are three SPDX patches for 5.7-rc1.
One fixes up the SPDX tag for a single driver, while the other two go
through the tree and add SPDX tags for all of the .gitignore files as
needed.
Nothing too complex, but you will get a merge conflict with your
current tree, that should be trivial to handle (one file modified by
two things, one file deleted.)
All three of these have been in linux-next for a while, with no
reported issues other than the merge conflict"
* tag 'spdx-5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/spdx:
ASoC: MT6660: make spdxcheck.py happy
.gitignore: add SPDX License Identifier
.gitignore: remove too obvious comments
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Add SPDX License Identifier to all .gitignore files.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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'kfree_rcu.2020.02.20a', 'locktorture.2020.02.20a', 'ovld.2020.02.20a', 'rcu-tasks.2020.02.20a', 'srcu.2020.02.20a' and 'torture.2020.02.20a' into HEAD
doc.2020.02.27a: Documentation updates.
fixes.2020.03.21a: Miscellaneous fixes.
kfree_rcu.2020.02.20a: Updates to kfree_rcu().
locktorture.2020.02.20a: Lock torture-test updates.
ovld.2020.02.20a: Updates to callback-overload handling.
rcu-tasks.2020.02.20a: RCU-tasks updates.
srcu.2020.02.20a: SRCU updates.
torture.2020.02.20a: Torture-test updates.
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This commit enables the KCSAN Kconfig options that (1) detect data
races between reads and writes even when the writes do not change the
variable's value and (2) detect data races involving plain C-language
writes. These changes only affect scripted rcutorture runs and can be
overridden using the kvm.sh --kconfig argument.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, kvm-find-errors.sh gives a usage prompt when given a bad
directory, but then soldiers on, giving a series of confusing error
messages. This commit therefore prints an error message and exits when
given a bad directory, hopefully reducing confusion.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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When running the default list of tests, the run summary of a successful
(that is, failed to find any errors) run fits easily on a 24-line screen.
But a run with something like "--configs '5*CFLIST'" will be 80 lines long,
and it is all too easy to miss a failure message when scrolling back.
This commit therefore prints out the number of runs with failing builds
or runtime failures, but only if there are any such failures.
For example, a run with a single build error and a single runtime error
would print two lines like this:
1 runs with build errors.
1 runs with runtime errors.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The small-system rcutorture configurations have served us well for a great
many years, but it is now time to add a larger one. This commit does
just that, but does not add it to the defaults in CFLIST. This allows
the kvm.sh argument '--configs "4*CFLIST TREE10" to run four instances
of each of the default configurations concurrently with one instance of
the large configuration.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The names of the per-test results directories are of the form
2019.11.29-20:42:19. This works, but the ":" characters make
tab-based shell name completion a bit onerous because the user must
remember to include a quote character somewhere before the first ":".
This commit therefore changes the ":" characters to periods, as in
2019.12.01-20.48.01", which allows tab-based completion to work more
naturally.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The bootparam_hotplug_cpu() bash function was checking for CPU-hotplug
kernel-boot parameters from --bootargs, but that check was specific to
rcutorture ("rcutorture\.onoff_"). This commit therefore makes this
check also work for locktorture ("torture\.onoff_").
Note that rcuperf does not do CPU-hotplug operations, so it is not
necessary to make a similar change for rcuperf.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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On some kernels, concurrent calls to the lscpu command result in severe
slowdowns. For example, on v4.16, a single lscpu invocation takes about
two milliseconds, four concurrent invocations more than two seconds,
and 16 concurrent invocations more than 20 seconds. Given that the only
goal is to learn the number of CPUs, invoking lscpu but once suffices.
This commit therefore invokes lscpu early in kvm.sh execution, setting
the initial value of the TORTURE_ALLOTED_CPUS environment variable.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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On a large system, it can be convenient to tell rcutorture to run
several instances of the default scenarios. Currently, this requires
explicitly listing them, for example, "--configs '2*SRCU-N 2*SRCU-P...'".
Although this works, it is rather inconvenient.
This commit therefore allows "CFLIST" to be specified to indicate the
default list of scenarios called out in the relevant CFLIST file, for
example, for RCU, tools/testing/selftests/rcutorture/configs/rcu/CFLIST.
In addition, multipliers may be used to run multiple instances of all
the scenarios. For example, on a 256-CPU system, "--configs '3*CFLIST'"
would run three instances of each scenario concurrently with one CPU
left over. Thus "--configs '3*CFLIST TINY01'" would exactly consume all
256 CPUs, which makes rcutorture's jitter feature more effective.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds the worst-case results from any call_rcu()
forward-progress tests to the rcutorture test-summary output.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The rcutorture scripting uses the mpstat command to determine how much
the system is being used, and adjusts make's -j argument accordingly.
However, mpstat isn't installed by default, so it would be good if the
scripting does something useful when mpstat isn't present.
This commit therefore makes the scripts assumes that if mpstat is not
present, they are free to use all the CPUs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, jitter.sh assumes that the underlying hypervisor will be
configured with all CPUs hotpluggable, with the possible exception
of CPU 0. However, there are installations where the hypervisor
prohibits offlining, which breaks jitter.sh. This commit therefore
lists the CPUs that cannot be offlined up front, and checks for the
case where no CPU can be offlined in the loop.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The dracut scripting does not work on all platforms, and there are no
known failures from the init binary based on the statically linked C
program. This commit therefore removes the dracut scripting so that the
statically linked C program is always used to create the init "script".
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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In many environments, gawk provides systime(), but awk doesn't.
This commit therefore changes awk scripts using systime() to instead be
gawk scripts.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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A number of mainstream CPU families are no longer capable of building
kernels having CONFIG_SMP=y and CONFIG_HOTPLUG_CPU=n, so this commit
removes this combination from the rcutorture scenarios having it.
People wishing to try out this combination may still do so using the
"--kconfig CONFIG_HOTPLUG_CPU=n CONFIG_SUSPEND=n CONFIG_HIBERNATION=n"
argument to the tools/testing/selftests/rcutorture/bin/kvm.sh script
that is used to run rcutorture.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Since commit 05f415715ce45 ("rcu: Speed up expedited GPs when interrupting
RCU reader") in v5.0 and through v5.1, booting with the threadirqs kernel
boot parameter caused self-deadlocks, which can be reproduced using the
following command on an 8-CPU system:
tools/testing/selftests/rcutorture/bin/kvm.sh --duration 5 --configs "TREE03" --bootargs "threadirqs"
This commit therefore adds the threadirqs kernel boot parameter to
the TREE03 rcutorture scenario in order to more quickly detect future
similar bugs.
Link: http://lkml.kernel.org/r/20190626135447.y24mvfuid5fifwjc@linutronix.de
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Joel Fernandes <joel@joelfernandes.org>
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The kvm-test-1-run.sh script says 'test -z "last_ts"' which always
evaluates to true (AKA zero) regardless of the value of the last_ts shell
variable. This commit therefore inserts the needed dollar sign ("$").
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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When trace_printk() is used, a message including "BUG" is printed to
the console, which fools the rcutorture scripting into believing that
the corresponding test scenario failed. This commit therefore filters
out this particular instance of "BUG", thus avoiding the false-positive
test-failure report.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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The current rcutorture scripts unconditionally do "make clean", which is
a good way of getting the needed testing done despite any imperfections in
Makefile dependency tracking. However, this can be a bit irritating when
repeatedly running a single scenario after small changes, for example,
when debugging a problem that affects only a single scenario. This commit
therefore adds a --trust-make argument that suppresses the "make clean".
Even when using ccache, this speeds up kernel builds by up to almost an
order of magnitude on my laptop.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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Currently, rcutorture will use relatively few CPUs to build the kernel
on a busy system, which is often as it should be. However, if the user
has used the --cpus argument to dedicate a specified number of CPUs to
this torture test, it would be good if the kernel build also made use
of them. This commit therefore changes the cpus2use.sh script to use
--cpus when specified and to do the idleness calculations otherwise.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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For historical reasons, rcutorture places its build products in a
tools/testing/selftests/rcutorture/b1 directory using the O= kbuild
command-line argument. However, doing this requires that the source
directory be pristine: Not just "make clean" pristine, but instead "make
mrproper" (or, equivalently, "make distclean") pristine. Therefore,
rcutorture executes a "make mrproper" before each build. Unfortunately,
"make mrproper" has the side effect of removing pretty much everything,
including tags files and cscope databases, which can be inconvenient
to people whose workflow centers around a single source tree.
This commit therefore makes rcutorture do the build directly in the
source directory, removing the need for "make mrproper". This works
because all needed build products are moved to their proper place in the
"res" directory immediately after the build completes, so that multiple
rcutorture kernels can still run concurrently.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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Currently qemu output appears on standard output, but is inaccessible
later on. This commit therefore captures this output and causes
kvm-recheck.sh to output this output if QEMU gave a non-zero non-137
exit code. (And exit code of 137 indicates that QEMU was killed, in
which case we want to know about the hang rather than the fact that
QEMU was killed.)
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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In one of my rcutorture tests the TSC clocksource got marked unstable
due to a large difference in the TSC value. I'm not sure if the guest
run for a long time with disabled interrupts or if the host was very
busy and didn't schedule the guest for some time.
I took a look on the qemu/KVM options and decided to update the options:
- Use kvm{32|64} as CPU. We could probably use `host' (like ARM does)
for maximum available features but since we don't run any userland I'm
not sure if it makes any difference.
- Drop the "noapic" option. There is no history why the APIC was disabled,
I see no reason for it. Once old qemu versions fade away, we can add
"x2apic=on,tsc-deadline=on,hypervisor=on,tsc_adjust=on".
- Additional config options. It ensures that the kernel knowns that it
runs as a kvm guest and can use virt devices like the kvm-clock as
clocksource. The kvm-clock was the main motivation here.
- I didn't add a random HW device. It would make the random device ready
earlier (not it doesn't complete the initialisation at all) but I
doubt that there is any need for this.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ paulmck: The world is not quite ready for CONFIG_PARAVIRT_SPINLOCKS=y
and x2apic, so they are omitted for the time being. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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I have been showing off a trivial RCU implementation for non-preemptive
environments for some time now:
#define rcu_read_lock()
#define rcu_read_unlock()
#define rcu_dereference(p) READ_ONCE(p)
#define rcu_assign_pointer(p, v) smp_store_release(&(p), (v))
void synchronize_rcu(void)
{
int cpu;
for_each_online_cpu(cpu)
sched_setaffinity(current->pid, cpumask_of(cpu));
}
Trivial or not, as the old saying goes, "if it ain't tested, it don't
work!". This commit therefore adds a "trivial" flavor to rcutorture
and a corresponding TRIVIAL test scenario. This variant does not handle
CPU hotplug, which is unconditionally enabled on x86 for post-v5.1-rc3
kernels, which is why the TRIVIAL.boot says "rcutorture.onoff_interval=0".
This commit actually does handle CONFIG_PREEMPT=y kernels, but only
because it turns back the Linux-kernel clock in order to provide these
alternative definitions (or the moral equivalent thereof):
#define rcu_read_lock() preempt_disable()
#define rcu_read_unlock() preempt_enable()
In CONFIG_PREEMPT=n kernels without debugging, these are equivalent to
empty macros give or take a compiler barrier. However, the have been
successfully tested with actual empty macros as well.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Fix symbol issue reported by kbuild test robot <lkp@intel.com>. ]
[ paulmck: Work around sched_setaffinity() issue noted by Andrea Parri. ]
[ paulmck: Add rcutorture.shuffle_interval=0 to TRIVIAL.boot to fix
interaction with shuffler task noted by Peter Zijlstra. ]
Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
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Because TREE01 can end up running more vCPUs that physical CPUs,
hammering these shortchanged CPUs with tight loops containing call_rcu()
invocations seems a bit like overkill. This commit therefore exempts
TREE01 from rcutorture's forward-progress testing.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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This commit provides a rudimentary Makefile that runs a 10-minute
rcutorture test on scenario TREE01. This must be run on a system capable
of spawning virtual machines and with everything installed to permit
building Linux kernels.
Reported-by: Shuah Khan <shuah@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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This commit causes both kvm-find-errors.sh and kvm-recheck.sh to provide
an exit status based on whether or not errors were located. In the
case of kvm-recheck.sh, this will be the error status of the last run.
This change allows these commands to be used in scripting and Makefiles
to automatically report failed rcutorture runs.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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jitter.sh currently does not add CPU0 to the list of CPUs for adding of
jitter. Let us add it to this list even when it is not hot-pluggable.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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The rcutorture jitter.sh script selects a random CPU but does not check
if it is offline or online. This leads to taskset errors many times. On
my machine, hyper threading is disabled so half the cores are offline
causing taskset errors a lot of times. Let us fix this by checking from
only the online CPUs on the system.
Cc: rcu@vger.kernel.org
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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Pull block updates from Jens Axboe:
"Nothing major in this series, just fixes and improvements all over the
map. This contains:
- Series of fixes for sed-opal (David, Jonas)
- Fixes and performance tweaks for BFQ (via Paolo)
- Set of fixes for bcache (via Coly)
- Set of fixes for md (via Song)
- Enabling multi-page for passthrough requests (Ming)
- Queue release fix series (Ming)
- Device notification improvements (Martin)
- Propagate underlying device rotational status in loop (Holger)
- Removal of mtip32xx trim support, which has been disabled for years
(Christoph)
- Improvement and cleanup of nvme command handling (Christoph)
- Add block SPDX tags (Christoph)
- Cleanup/hardening of bio/bvec iteration (Christoph)
- A few NVMe pull requests (Christoph)
- Removal of CONFIG_LBDAF (Christoph)
- Various little fixes here and there"
* tag 'for-5.2/block-20190507' of git://git.kernel.dk/linux-block: (164 commits)
block: fix mismerge in bvec_advance
block: don't drain in-progress dispatch in blk_cleanup_queue()
blk-mq: move cancel of hctx->run_work into blk_mq_hw_sysfs_release
blk-mq: always free hctx after request queue is freed
blk-mq: split blk_mq_alloc_and_init_hctx into two parts
blk-mq: free hw queue's resource in hctx's release handler
blk-mq: move cancel of requeue_work into blk_mq_release
blk-mq: grab .q_usage_counter when queuing request from plug code path
block: fix function name in comment
nvmet: protect discovery change log event list iteration
nvme: mark nvme_core_init and nvme_core_exit static
nvme: move command size checks to the core
nvme-fabrics: check more command sizes
nvme-pci: check more command sizes
nvme-pci: remove an unneeded variable initialization
nvme-pci: unquiesce admin queue on shutdown
nvme-pci: shutdown on timeout during deletion
nvme-pci: fix psdt field for single segment sgls
nvme-multipath: don't print ANA group state by default
nvme-multipath: split bios with the ns_head bio_set before submitting
...
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Currently support for 64-bit sector_t and blkcnt_t is optional on 32-bit
architectures. These types are required to support block device and/or
file sizes larger than 2 TiB, and have generally defaulted to on for
a long time. Enabling the option only increases the i386 tinyconfig
size by 145 bytes, and many data structures already always use
64-bit values for their in-core and on-disk data structures anyway,
so there should not be a large change in dynamic memory usage either.
Dropping this option removes a somewhat weird non-default config that
has cause various bugs or compiler warnings when actually used.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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The scripting must supply the CONFIG_INITRAMFS_SOURCE Kconfig option
so that kbuild can find the desired initrd, but the configcheck.sh
script gets confused by this option because it takes a string instead
of the expected y/n/m. This causes checkconfig.sh to complain about
CONFIG_INITRAMFS_SOURCE in the torture-test output (though not in the
summary). As more people use rcutorture, the resulting confusion is
an increasing concern.
This commit therefore suppresses this false-positive warning by filtering
CONFIG_INITRAMFS_SOURCE from within the checkconfig.sh script.
Reported-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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Replace the license boiler plate with a SPDX license identifier.
While in the area, update an email address and add copyright notices.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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As suggested by Ingo, this header file might benefit other tools than
just rcutorture. For now it's quite limited, but is easy to extend, so
exposing it into tools/include/nolibc/ will make it much easier to
adopt by other tools.
The mkinitrd.sh script in rcutorture was updated to use this new location.
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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Ingo rightfully asked for a bit more documentation in the nolibc header,
so this patch adds some explanation about its purpose, how it's made, and
how to use it.
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Reviewed-by: Joey Pabalinas <joeypabalinas@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
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A few macros had their rightmost backslash misaligned, and the pollfd
struct definition resisted the previous code reindent. Nothing else
changed.
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Reviewed-by: Joey Pabalinas <joeypabalinas@gmail.com>
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A last-minute checkpatch cleanup caused most of list of clobbered
registers to be lost in the MIPS syscall definition. Although this code
is not yet used on MIPS, it is nevertheless better to fix it before it
does get used.
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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Why a Bourne-shell "for" loop? And why 192 instances of "a"? This commit
adds a shell comment to present the answer to these mysteries. It also
uses a series of factor-of-four Bourne-shell assignments to make it
easy to see how many instances there are, replacing the earlier wall of
'a' characters.
Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
[ paulmck: Fix wrong-variable bugs noted by Andrea Parri. ]
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'doc.2018.11.12a', 'fixes.2018.11.12a', 'initrd.2018.11.08b', 'sil.2018.11.12a' and 'srcu.2018.11.27a' into HEAD
bug.2018.11.12a: Get rid of BUG_ON() and friends
consolidate.2018.12.01a: Continued RCU flavor-consolidation cleanup
doc.2018.11.12a: Documentation updates
fixes.2018.11.12a: Miscellaneous fixes
initrd.2018.11.08b: Automate creation of rcutorture initrd
sil.2018.11.12a: Remove more spin_unlock_wait() calls
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Now that synchronize_rcu() waits for preempt-disable regions of code
as well as RCU read-side critical sections, synchronize_sched() can be
replaced by synchronize_rcu(). This commit therefore makes this change,
even though it is but a comment.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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This reduces the size of the init executable from ~800 kB to ~800 bytes
on x86_64. This is only implemented for x86_64, i386, arm and arm64.
Others not tested.
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This is a definition of the most common syscalls needed in minimalist
init executables, allowing to statically build them with no external
dependencies. It is sufficient in its current form to build rcutorture's
init on x86_64, i386, arm, and arm64. Others have not been ported or
tested. Updates may be found here :
http://git.formilux.org/?p=people/willy/nolibc.git
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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If the build fails, we can end up with an empty initrd directory which
prevents the build script from operating again. Better rely on the
resulting init executable instead.
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Strip using -s on the compiler command line instead of calling the "strip"
utility as the latter isn't necessarily compatible with the target arch.
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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This adds the CROSS_COMPILE environment to the initrd.sh script's
gcc command to enable cross compilation.
Reported-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Currently, the initrd/init script and executable remain blocked almost
all the time. However, it is necessary to test nohz_full userspace
execution, which both variants of initrd/init fail to do. This commit
therefore causes initrd/init to spend about a millisecond per second
executing in userspace.
Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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The support for creating initrd directories using dracut is a great
improvement over having to always hand-create them, it is a bit annoying
to have to install some otherwise irrelevant package just to be able to
run rcutorture. This commit therefore adds support for creating initrd
directories on systems innocent of dracut. You do need gcc, but then
again you need that to build the kernel (or to build llvm) in any case.
The idea is to create an initrd directory containing nothing but a
statically linked binary having a for-loop over a long-term sleep().
The result is a Linux kernel with almost no userspace: even the
time-honored /dev, /lib, /tmp, and /usr directories are gone. In fact,
the only directory present is "/", but only because I don't know how to
get rid of it, at least short of not having an initrd in the first place.
Although statically linked binaries are much maligned, and rightly so,
their disadvantages seem to be irrelevant for this particular use case.
From https://www.akkadia.org/drepper/no_static_linking.html:
1. Fixes are difficult to apply to hordes of widely scattered
statically linked binaries. But in this case, there is only one
binary, but there would otherwise be no fewer than four libraries.
2. Security measures like local address randomization cannot be used.
Prudence prevents me from asserting that it is impossible to
base a remote attack on a networking-free rcutorture instance.
Nevertheless, bonus points to the first person who comes up with
such an attack!
3. More efficient use of physical memory. Not in this case, given
that libc is 1.8MB and the statically linked binary "only" 800K.
4. Features such as locales, name service switch (NSS),
internationalized domain names (IDN) tool, and so on require
dynamic linking. Bonus points to the first person coming up
with a valid rcutorture use case requiring these features in
its initrd.
5. Accidental violations of (L)GPL. Actually, this change actually
helps -avoid- such violations by reducing the temptation to
pass around tarballs of rcutorture-ready initrd directories.
After all, the rcutorture scripts automatically create an initrd
directory for you, so why bother with the tarballs?
6. Tools and hacks like ltrace, LD_PRELOAD, LD_PROFILE, and LD_AUDIT
don't work. Again, bonus points to the first person coming up
with a valid rcutorture use case requiring these features in
its initrd.
Nevertheless, the script will use dracut if available, and will create the
statically linked binary only when dracut are missing. Those preferring
the smaller initrd directory resulting from the statically linked binary
(like me) are free to hand-edit mkinitrd.sh to remove the code using
dracut. ;-)
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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