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Subject[tip:x86/urgent] x86/debug: Handle warnings before the notifier chain, to fix KGDB crash
Commit-ID:  b8347c2196492f4e1cccde3d92fda1cc2cc7de7e
Gitweb: https://git.kernel.org/tip/b8347c2196492f4e1cccde3d92fda1cc2cc7de7e
Author: Alexander Shishkin <alexander.shishkin@linux.intel.com>
AuthorDate: Mon, 24 Jul 2017 13:04:28 +0300
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 10 Nov 2017 08:04:19 +0100

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

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@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>
---
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 67db4f4..5a6b8f8 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -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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