The patch titled
Subject: dump_stack: avoid the livelock of the dump_lock
has been added to the -mm tree. Its filename is
dump_stack-avoid-the-livelock-of-the-dump_lock.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dump_stack-avoid-the-livelock-of-the-dump_lock.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dump_stack-avoid-the-livelock-of-the-dump_lock.patch
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------------------------------------------------------
From: Kevin Hao <haokexin@xxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20191030031637.6025-1-haokexin@xxxxxxxxx
Fixes: b58d977432c8 ("dump_stack: serialize the output from dump_stack()")
Signed-off-by: Kevin Hao <haokexin@xxxxxxxxx>
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/dump_stack.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/lib/dump_stack.c~dump_stack-avoid-the-livelock-of-the-dump_lock
+++ a/lib/dump_stack.c
@@ -106,7 +106,11 @@ retry:
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;
}
_
Patches currently in -mm which might be from haokexin@xxxxxxxxx are
dump_stack-avoid-the-livelock-of-the-dump_lock.patch
