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authorLuis R. Rodriguez <mcgrof@kernel.org>2017-07-14 14:50:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-14 15:05:13 -0700
commit6d7964a722afc8e4f880b947f174009063028c99 (patch)
tree6b5ff5d40ee75f72396a67f93ddbfee752e7cac0 /kernel
parentd9c6a72d6fa29d3a7999dda726577e5d1fccafa5 (diff)
kmod: throttle kmod thread limit
If we reach the limit of modprobe_limit threads running the next request_module() call will fail. The original reason for adding a kill was to do away with possible issues with in old circumstances which would create a recursive series of request_module() calls. We can do better than just be super aggressive and reject calls once we've reached the limit by simply making pending callers wait until the threshold has been reduced, and then throttling them in, one by one. This throttling enables requests over the kmod concurrent limit to be processed once a pending request completes. Only the first item queued up to wait is woken up. The assumption here is once a task is woken it will have no other option to also kick the queue to check if there are more pending tasks -- regardless of whether or not it was successful. By throttling and processing only max kmod concurrent tasks we ensure we avoid unexpected fatal request_module() calls, and we keep memory consumption on module loading to a minimum. With x86_64 qemu, with 4 cores, 4 GiB of RAM it takes the following run time to run both tests: time ./kmod.sh -t 0008 real 0m16.366s user 0m0.883s sys 0m8.916s time ./kmod.sh -t 0009 real 0m50.803s user 0m0.791s sys 0m9.852s Link: http://lkml.kernel.org/r/20170628223155.26472-4-mcgrof@kernel.org Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org> Reviewed-by: Petr Mladek <pmladek@suse.com> Cc: Jessica Yu <jeyu@redhat.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Michal Marek <mmarek@suse.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/kmod.c16
1 files changed, 7 insertions, 9 deletions
diff --git a/kernel/kmod.c b/kernel/kmod.c
index ff68198fe83b..6d016c5d97c8 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -68,6 +68,7 @@ static DECLARE_RWSEM(umhelper_sem);
*/
#define MAX_KMOD_CONCURRENT 50
static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);
+static DECLARE_WAIT_QUEUE_HEAD(kmod_wq);
/*
modprobe_path is set via /proc/sys.
@@ -140,7 +141,6 @@ int __request_module(bool wait, const char *fmt, ...)
va_list args;
char module_name[MODULE_NAME_LEN];
int ret;
- static int kmod_loop_msg;
/*
* We don't allow synchronous module loading from async. Module
@@ -164,14 +164,11 @@ int __request_module(bool wait, const char *fmt, ...)
return ret;
if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {
- /* We may be blaming an innocent here, but unlikely */
- if (kmod_loop_msg < 5) {
- printk(KERN_ERR
- "request_module: runaway loop modprobe %s\n",
- module_name);
- kmod_loop_msg++;
- }
- return -ENOMEM;
+ pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...",
+ atomic_read(&kmod_concurrent_max),
+ MAX_KMOD_CONCURRENT, module_name);
+ wait_event_interruptible(kmod_wq,
+ atomic_dec_if_positive(&kmod_concurrent_max) >= 0);
}
trace_module_request(module_name, wait, _RET_IP_);
@@ -179,6 +176,7 @@ int __request_module(bool wait, const char *fmt, ...)
ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
atomic_inc(&kmod_concurrent_max);
+ wake_up(&kmod_wq);
return ret;
}