From 93e13a360ba331915220f82f6e9543df961ffa1f Mon Sep 17 00:00:00 2001 From: Michael Holzheu Date: Thu, 12 Jan 2012 17:20:18 -0800 Subject: [PATCH] kdump: fix crash_kexec()/smp_send_stop() race in panic() When two CPUs call panic at the same time there is a possible race condition that can stop kdump. The first CPU calls crash_kexec() and the second CPU calls smp_send_stop() in panic() before crash_kexec() finished on the first CPU. So the second CPU stops the first CPU and therefore kdump fails: 1st CPU: panic()->crash_kexec()->mutex_trylock(&kexec_mutex)-> do kdump 2nd CPU: panic()->crash_kexec()->kexec_mutex already held by 1st CPU ->smp_send_stop()-> stop 1st CPU (stop kdump) This patch fixes the problem by introducing a spinlock in panic that allows only one CPU to process crash_kexec() and the subsequent panic code. All other CPUs call the weak function panic_smp_self_stop() that stops the CPU itself. This function can be overloaded by architecture code. For example "tile" can use their lower-power "nap" instruction for that. Signed-off-by: Michael Holzheu Acked-by: Chris Metcalf Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/panic.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/kernel/panic.c b/kernel/panic.c index 6fd09ed6fd90..5dce5404eeef 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -49,6 +49,15 @@ static long no_blink(int state) long (*panic_blink)(int state); EXPORT_SYMBOL(panic_blink); +/* + * Stop ourself in panic -- architecture code may override this + */ +void __weak panic_smp_self_stop(void) +{ + while (1) + cpu_relax(); +} + /** * panic - halt the system * @fmt: The text string to print @@ -59,6 +68,7 @@ EXPORT_SYMBOL(panic_blink); */ void panic(const char *fmt, ...) { + static DEFINE_SPINLOCK(panic_lock); static char buf[1024]; va_list args; long i, i_next = 0; @@ -68,8 +78,14 @@ void panic(const char *fmt, ...) * It's possible to come here directly from a panic-assertion and * not have preempt disabled. Some functions called from here want * preempt to be disabled. No point enabling it later though... + * + * Only one CPU is allowed to execute the panic code from here. For + * multiple parallel invocations of panic, all other CPUs either + * stop themself or will wait until they are stopped by the 1st CPU + * with smp_send_stop(). */ - preempt_disable(); + if (!spin_trylock(&panic_lock)) + panic_smp_self_stop(); console_verbose(); bust_spinlocks(1);