Commit f0a996ee authored Aug 10, 2012 by Jason Wessel

mips,kgdb: fix recursive page fault with CONFIG_KPROBES



This fault was detected using the kgdb test suite on boot and it
crashes recursively due to the fact that CONFIG_KPROBES on mips adds
an extra die notifier in the page fault handler.  The crash signature
looks like this:

kgdbts:RUN bad memory access test
KGDB: re-enter exception: ALL breakpoints killed
Call Trace:
[<807b7548>] dump_stack+0x20/0x54
[<807b7548>] dump_stack+0x20/0x54

The fix for now is to have kgdb return immediately if the fault type
is DIE_PAGE_FAULT and allow the kprobe code to decide what is supposed
to happen.

Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

parent f30fed10

arch/mips/kernel/kgdb.c

+9 −0

Original line number	Original line	Diff line number	Diff line
	@@ -283,6 +283,15 @@ static int kgdb_mips_notify(struct notifier_block *self, unsigned long cmd,
	struct pt_regs *regs = args->regs;		struct pt_regs *regs = args->regs;
	int trap = (regs->cp0_cause & 0x7c) >> 2;		int trap = (regs->cp0_cause & 0x7c) >> 2;

			#ifdef CONFIG_KPROBES
			/*
			* Return immediately if the kprobes fault notifier has set
			* DIE_PAGE_FAULT.
			*/
			if (cmd == DIE_PAGE_FAULT)
			return NOTIFY_DONE;
			#endif /* CONFIG_KPROBES */

	/* Userspace events, ignore. */		/* Userspace events, ignore. */
	if (user_mode(regs))		if (user_mode(regs))
	return NOTIFY_DONE;		return NOTIFY_DONE;

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