Re: [PATCH] Fix BUG: using smp_processor_id() in preemptible codein print_fatal_signal()

From: Ed Swierk
Date: Mon Jan 26 2009 - 20:37:13 EST


On Tue, 2009-01-27 at 01:41 +0100, Oleg Nesterov wrote:
> Ed, Ingo, but isn't it better to just use raw_smp_processor_id() in
> __show_regs() ? This is only debug info, the printed CPU doesn't
> have the "exact" meaning.

I guess it doesn't really matter which CPU the signal handling thread
happened to be running on, but are there other situations where
show_regs() is always expected to print the correct CPU (and if not, why
bother printing the CPU at all)? Disabling preemption here seems the
safest approach and doesn't add much overhead.

> And, without the comment, it is not easy to see why print_fatal_signal()
> disables preeemption before show_regs().

Agreed; here's an updated patch.

Signed-off-by: Ed Swierk <eswierk@xxxxxxxxxxxxxxxxxx>

---
Index: linux-2.6.27.4/kernel/signal.c
===================================================================
--- linux-2.6.27.4.orig/kernel/signal.c
+++ linux-2.6.27.4/kernel/signal.c
@@ -890,7 +890,9 @@ static void print_fatal_signal(struct pt
}
#endif
printk("\n");
- show_regs(regs);
+ preempt_disable();
+ show_regs(regs); /* calls smp_processor_id(), preemption not allowed */
+ preempt_enable();
}

static int __init setup_print_fatal_signals(char *str)


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