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authorKevin Hao <haokexin@gmail.com>2019-11-05 21:16:57 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-11-06 08:47:50 -0800
commit5cbf2fff3bba8d3c6a4d47c1754de1cf57e2b01f (patch)
tree25bc30bf2caa8885f914a052558a8b2b62257ab4 /lib/dump_stack.c
parenta31631302abce4c80913d4dc741c4a6b07969b0e (diff)
dump_stack: avoid the livelock of the dump_lock
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. [akpm@linux-foundation.org: fix comment] Link: http://lkml.kernel.org/r/20191030031637.6025-1-haokexin@gmail.com Fixes: b58d977432c8 ("dump_stack: serialize the output from dump_stack()") Signed-off-by: Kevin Hao <haokexin@gmail.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/dump_stack.c')
-rw-r--r--lib/dump_stack.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 5cff72f18c4a..33ffbf308853 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -106,7 +106,12 @@ retry:
was_locked = 1;
} else {
local_irq_restore(flags);
- cpu_relax();
+ /*
+ * Wait for 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;
}