From 57f0060b8a2bb2a70a4cce1a37d5e0158cea92a6 Mon Sep 17 00:00:00 2001 From: Ralf Baechle Date: Thu, 10 Feb 2005 12:00:06 +0000 Subject: Document why calling smp_call_function will deadlock when called with interrupts disabled. Signed-off-by: Ralf Baechle --- arch/mips/kernel/smp.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c index af5cd3b8a39683..1d3a4b50194942 100644 --- a/arch/mips/kernel/smp.c +++ b/arch/mips/kernel/smp.c @@ -121,7 +121,19 @@ struct call_data_struct *call_data; * or are or have executed. * * You must not call this function with disabled interrupts or from a - * hardware interrupt handler or from a bottom half handler. + * hardware interrupt handler or from a bottom half handler: + * + * CPU A CPU B + * Disable interrupts + * smp_call_function() + * Take call_lock + * Send IPIs + * Wait for all cpus to acknowledge IPI + * CPU A has not responded, spin waiting + * for cpu A to respond, holding call_lock + * smp_call_function() + * Spin waiting for call_lock + * Deadlock Deadlock */ int smp_call_function (void (*func) (void *info), void *info, int retry, int wait) -- cgit 1.2.3-korg