Commit b8347c21 authored Jul 24, 2017 by Alexander Shishkin Committed by Ingo Molnar Nov 10, 2017

x86/debug: Handle warnings before the notifier chain, to fix KGDB crash



Commit:

  9a93848f ("x86/debug: Implement __WARN() using UD0")

turned warnings into UD0, but the fixup code only runs after the
notify_die() chain. This is a problem, in particular, with kgdb,
which kicks in as if it was a BUG().

Fix this by running the fixup code before the notifier chain in
the invalid op handler path.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Tested-by: Ilya Dryomov <idryomov@gmail.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Cc: <stable@vger.kernel.org> # v4.12+
Link: http://lkml.kernel.org/r/20170724100428.19173-1-alexander.shishkin@linux.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent be739f4b

arch/x86/kernel/traps.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -209,9 +209,6 @@ do_trap_no_signal(struct task_struct tsk, int trapnr, char str,
		if (fixup_exception(regs, trapnr))
		return 0;

		if (fixup_bug(regs, trapnr))
		return 0;

		tsk->thread.error_code = error_code;
		tsk->thread.trap_nr = trapnr;
		die(str, regs, error_code);
		@@ -292,6 +289,13 @@ static void do_error_trap(struct pt_regs regs, long error_code, char str,

		RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");

		/*
		* WARN*()s end up here; fix them up before we call the
		* notifier chain.
		*/
		if (!user_mode(regs) && fixup_bug(regs, trapnr))
		return;

		if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
		NOTIFY_STOP) {
		cond_local_irq_enable(regs);

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