Messages in this thread Patch in this message | | | From | Kevin Hao <> | Subject | [PATCH v2] dump_stack: Avoid the livelock of the dump_lock | Date | Wed, 30 Oct 2019 11:16:37 +0800 |
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In the current code, we use the atomic_cmpxchg() to serialize the output of the dump_stack(), but this implementation suffers the thundering herd problem. We have observed such kind of livelock on a Marvell cn96xx board(24 cpus) when heavily using the dump_stack() in a kprobe handler. Actually we can let the competitors to wait for the releasing of the lock before jumping to atomic_cmpxchg(). This will definitely mitigate the thundering herd problem. Thanks Linus for the suggestion.
Fixes: b58d977432c8 ("dump_stack: serialize the output from dump_stack()") Cc: stable@vger.kernel.org Signed-off-by: Kevin Hao <haokexin@gmail.com> --- v2: 1. Use the method suggested by Linus. 2. Since this fix seems pretty simple, maybe it deserve to be backported to stable kernel. So CC the stable.
lib/dump_stack.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/lib/dump_stack.c b/lib/dump_stack.c index 5cff72f18c4a..0062dfcafd63 100644 --- a/lib/dump_stack.c +++ b/lib/dump_stack.c @@ -106,7 +106,11 @@ asmlinkage __visible void dump_stack(void) was_locked = 1; } else { local_irq_restore(flags); - cpu_relax(); + /* + * Wait the lock to release before jumping to atomic_cmpxchg() + * in order to mitigate the thundering herd problem. + */ + do { cpu_relax(); } while (atomic_read(&dump_lock) != -1); goto retry; } -- 2.14.4
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