[ 3.5.yuz extended stable ] Patch "mips, kgdb: fix recursive page fault with CONFIG_KPROBES" has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Thu Nov 15 05:50:13 UTC 2012

This is a note to let you know that I have just added a patch titled

    mips,kgdb: fix recursive page fault with CONFIG_KPROBES

to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.yuz tree, see



>From eb7ed4610e1414991c1225c0c497476fd1140487 Mon Sep 17 00:00:00 2001
From: Jason Wessel <jason.wessel at windriver.com>
Date: Fri, 10 Aug 2012 12:21:15 -0500
Subject: [PATCH] mips,kgdb: fix recursive page fault with CONFIG_KPROBES

commit f0a996eeeda214f4293e234df33b29bec003b536 upstream.

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 at hitachi.com>
Cc: David S. Miller <davem at davemloft.net>
Signed-off-by: Jason Wessel <jason.wessel at windriver.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 arch/mips/kernel/kgdb.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/mips/kernel/kgdb.c b/arch/mips/kernel/kgdb.c
index f4546e9..23817a6 100644
--- a/arch/mips/kernel/kgdb.c
+++ b/arch/mips/kernel/kgdb.c
@@ -283,6 +283,15 @@ static int kgdb_mips_notify(struct notifier_block *self, unsigned long cmd,
 	struct pt_regs *regs = args->regs;
 	int trap = (regs->cp0_cause & 0x7c) >> 2;

+	/*
+	 * Return immediately if the kprobes fault notifier has set
+	 */
+	if (cmd == DIE_PAGE_FAULT)
+		return NOTIFY_DONE;
+#endif /* CONFIG_KPROBES */
 	/* Userspace events, ignore. */
 	if (user_mode(regs))
 		return NOTIFY_DONE;

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