[PATCH 24/72] panic: fix a possible deadlock in panic()
luis.henriques at canonical.com
Thu Apr 18 09:16:09 UTC 2013
18.104.22.168 -stable review patch. If anyone has any objections, please let me know.
From: Vikram Mulukutla <markivx at codeaurora.org>
commit 190320c3b6640d4104650f55ff69611e050ea06b upstream.
panic_lock is meant to ensure that panic processing takes place only on
one cpu; if any of the other cpus encounter a panic, they will spin
waiting to be shut down.
However, this causes a regression in this scenario:
1. Cpu 0 encounters a panic and acquires the panic_lock
and proceeds with the panic processing.
2. There is an interrupt on cpu 0 that also encounters
an error condition and invokes panic.
3. This second invocation fails to acquire the panic_lock
and enters the infinite while loop in panic_smp_self_stop.
Thus all panic processing is stopped, and the cpu is stuck for eternity
in the while(1) inside panic_smp_self_stop.
To address this, disable local interrupts with local_irq_disable before
acquiring the panic_lock. This will prevent interrupt handlers from
executing during the panic processing, thus avoiding this particular
Signed-off-by: Vikram Mulukutla <markivx at codeaurora.org>
Reviewed-by: Stephen Boyd <sboyd at codeaurora.org>
Cc: Michael Holzheu <holzheu at linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
kernel/panic.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/panic.c b/kernel/panic.c
index d2a5f4e..e1b2822 100644
@@ -75,6 +75,14 @@ void panic(const char *fmt, ...)
int state = 0;
+ * Disable local interrupts. This will prevent panic_smp_self_stop
+ * from deadlocking the first cpu that invokes the panic, since
+ * there is nothing to prevent an interrupt handler (that runs
+ * after the panic_lock is acquired) from invoking panic again.
* 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...
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