diff options
author | Michael Holzheu <holzheu@linux.vnet.ibm.com> | 2012-01-12 17:20:18 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-01-12 20:13:11 -0800 |
commit | 93e13a360ba331915220f82f6e9543df961ffa1f (patch) | |
tree | 470c120ee5d3de69f46e62ec85452bee14e8d67c /kernel | |
parent | bec013c40bc89671d8d457944fdf7d2b8e79d651 (diff) | |
download | lwn-93e13a360ba331915220f82f6e9543df961ffa1f.tar.gz lwn-93e13a360ba331915220f82f6e9543df961ffa1f.zip |
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.c | 18 |
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); |