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e8b4d457b1
commit5cbf2fff3bupstream. 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:b58d977432("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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
71 lines
1.4 KiB
C
71 lines
1.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Provide a default dump_stack() function for architectures
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* which don't implement their own.
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*/
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/sched.h>
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#include <linux/sched/debug.h>
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#include <linux/smp.h>
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#include <linux/atomic.h>
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static void __dump_stack(void)
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{
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dump_stack_print_info(KERN_DEFAULT);
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show_stack(NULL, NULL);
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}
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/**
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* dump_stack - dump the current task information and its stack trace
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*
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* Architectures can override this implementation by implementing its own.
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*/
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#ifdef CONFIG_SMP
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static atomic_t dump_lock = ATOMIC_INIT(-1);
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asmlinkage __visible void dump_stack(void)
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{
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unsigned long flags;
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int was_locked;
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int old;
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int cpu;
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/*
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* Permit this cpu to perform nested stack dumps while serialising
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* against other CPUs
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*/
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retry:
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local_irq_save(flags);
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cpu = smp_processor_id();
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old = atomic_cmpxchg(&dump_lock, -1, cpu);
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if (old == -1) {
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was_locked = 0;
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} else if (old == cpu) {
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was_locked = 1;
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} else {
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local_irq_restore(flags);
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/*
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* Wait for the lock to release before jumping to
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* atomic_cmpxchg() in order to mitigate the thundering herd
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* problem.
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*/
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do { cpu_relax(); } while (atomic_read(&dump_lock) != -1);
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goto retry;
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}
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__dump_stack();
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if (!was_locked)
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atomic_set(&dump_lock, -1);
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local_irq_restore(flags);
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}
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#else
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asmlinkage __visible void dump_stack(void)
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{
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__dump_stack();
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}
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#endif
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EXPORT_SYMBOL(dump_stack);
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