linux-kernel - [PATCH] x86/debug: Handle warnings before the notifier chain

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Date:   Mon, 24 Jul 2017 13:04:28 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Richard Weinberger <richard.weinberger@...il.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/debug: Handle warnings before the notifier chain

Commit

  9a93848fe787 ("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@...ux.intel.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Richard Weinberger <richard.weinberger@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/traps.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bf54309b85..b2157d4a53 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -221,9 +221,6 @@ 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);
@@ -304,6 +301,13 @@ 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);
-- 
2.13.2