linux-kernel - [ 16/76] mips,kgdb: fix recursive page fault with CONFIG

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Message-Id: <20121019024352.714301043@linuxfoundation.org>
Date:	Thu, 18 Oct 2012 19:46:40 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk,
	Jason Wessel <jason.wessel@...driver.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 16/76] mips,kgdb: fix recursive page fault with CONFIG_KPROBES

3.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wessel <jason.wessel@...driver.com>

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.

Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/mips/kernel/kgdb.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/arch/mips/kernel/kgdb.c
+++ b/arch/mips/kernel/kgdb.c
@@ -283,6 +283,15 @@ static int kgdb_mips_notify(struct notif
 	struct pt_regs *regs = args->regs;
 	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. */
 	if (user_mode(regs))
 		return NOTIFY_DONE;


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