From 190320c3b6640d4104650f55ff69611e050ea06b Mon Sep 17 00:00:00 2001 From: Vikram Mulukutla Date: Mon, 30 Jul 2012 14:39:58 -0700 Subject: [PATCH] panic: fix a possible deadlock in panic() 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 Reviewed-by: Stephen Boyd Cc: Michael Holzheu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/panic.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/panic.c b/kernel/panic.c index d2a5f4ecc6d..e1b2822fff9 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -74,6 +74,14 @@ void panic(const char *fmt, ...) long i, i_next = 0; 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 -- 2.20.1