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authorMichael Holzheu <holzheu@linux.vnet.ibm.com>2012-01-12 17:20:18 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-12 20:13:11 -0800
commit93e13a360ba331915220f82f6e9543df961ffa1f (patch)
tree470c120ee5d3de69f46e62ec85452bee14e8d67c /kernel
parentbec013c40bc89671d8d457944fdf7d2b8e79d651 (diff)
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 <holzheu@linux.vnet.ibm.com> Acked-by: Chris Metcalf <cmetcalf@tilera.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/panic.c18
1 files changed, 17 insertions, 1 deletions
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);

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