5cbf2fff3b
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>
132 lines
3.2 KiB
C
132 lines
3.2 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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#include <linux/kexec.h>
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#include <linux/utsname.h>
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static char dump_stack_arch_desc_str[128];
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/**
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* dump_stack_set_arch_desc - set arch-specific str to show with task dumps
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* @fmt: printf-style format string
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* @...: arguments for the format string
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*
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* The configured string will be printed right after utsname during task
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* dumps. Usually used to add arch-specific system identifiers. If an
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* arch wants to make use of such an ID string, it should initialize this
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* as soon as possible during boot.
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*/
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void __init dump_stack_set_arch_desc(const char *fmt, ...)
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{
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va_list args;
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va_start(args, fmt);
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vsnprintf(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str),
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fmt, args);
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va_end(args);
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}
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/**
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* dump_stack_print_info - print generic debug info for dump_stack()
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* @log_lvl: log level
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*
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* Arch-specific dump_stack() implementations can use this function to
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* print out the same debug information as the generic dump_stack().
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*/
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void dump_stack_print_info(const char *log_lvl)
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{
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printk("%sCPU: %d PID: %d Comm: %.20s %s%s %s %.*s\n",
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log_lvl, raw_smp_processor_id(), current->pid, current->comm,
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kexec_crash_loaded() ? "Kdump: loaded " : "",
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print_tainted(),
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init_utsname()->release,
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(int)strcspn(init_utsname()->version, " "),
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init_utsname()->version);
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if (dump_stack_arch_desc_str[0] != '\0')
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printk("%sHardware name: %s\n",
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log_lvl, dump_stack_arch_desc_str);
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print_worker_info(log_lvl, current);
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}
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/**
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* show_regs_print_info - print generic debug info for show_regs()
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* @log_lvl: log level
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*
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* show_regs() implementations can use this function to print out generic
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* debug information.
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*/
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void show_regs_print_info(const char *log_lvl)
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{
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dump_stack_print_info(log_lvl);
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}
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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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