This is a note to let you know that I've just added the patch titled
panic: fix a possible deadlock in panic()
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
panic-fix-a-possible-deadlock-in-panic.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 190320c3b6640d4104650f55ff69611e050ea06b Mon Sep 17 00:00:00 2001
From: Vikram Mulukutla <markivx@xxxxxxxxxxxxxx>
Date: Mon, 30 Jul 2012 14:39:58 -0700
Subject: panic: fix a possible deadlock in panic()
From: Vikram Mulukutla <markivx@xxxxxxxxxxxxxx>
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
problem.
Signed-off-by: Vikram Mulukutla <markivx@xxxxxxxxxxxxxx>
Reviewed-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Cc: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/panic.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -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.
+ */
+ local_irq_disable();
+
+ /*
* 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...
Patches currently in stable-queue which might be from markivx@xxxxxxxxxxxxxx are
queue-3.4/panic-fix-a-possible-deadlock-in-panic.patch
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