The patch titled
Subject: kdump: fix crash_kexec()/smp_send_stop() race in panic
has been added to the -mm tree. Its filename is
kdump-fix-crash_kexec-smp_send_stop-race-in-panic.patch
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------------------------------------------------------
From: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>
Subject: 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.
Signed-off-by: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/panic.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff -puN kernel/panic.c~kdump-fix-crash_kexec-smp_send_stop-race-in-panic kernel/panic.c
--- a/kernel/panic.c~kdump-fix-crash_kexec-smp_send_stop-race-in-panic
+++ a/kernel/panic.c
@@ -59,6 +59,7 @@ EXPORT_SYMBOL(panic_blink);
*/
NORET_TYPE void panic(const char * fmt, ...)
{
+ static DEFINE_SPINLOCK(panic_lock);
static char buf[1024];
va_list args;
long i, i_next = 0;
@@ -82,6 +83,13 @@ NORET_TYPE void panic(const char * fmt,
#endif
/*
+ * Only one CPU is allowed to execute the panic code from here. For
+ * multiple parallel invocations of panic all other CPUs will wait on
+ * the panic_lock. They are stopped afterwards by smp_send_stop().
+ */
+ spin_lock(&panic_lock);
+
+ /*
* If we have crashed and we have a crash kernel loaded let it handle
* everything else.
* Do we want to call this before we try to display a message?
_
Subject: Subject: kdump: fix crash_kexec()/smp_send_stop() race in panic
Patches currently in -mm which might be from holzheu@xxxxxxxxxxxxxxxxxx are
linux-next.patch
lib-stringc-fix-strim-semantics-for-strings-that-have-only-blanks.patch
kdump-fix-crash_kexec-smp_send_stop-race-in-panic.patch
kdump-add-udev-events-for-memory-online-offline.patch
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