From: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
commit b8347c2196492f4e1cccde3d92fda1cc2cc7de7e upstream
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@xxxxxxxxxxxxxxx>
Tested-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Acked-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Richard Weinberger <richard.weinberger@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.12+
Link: http://lkml.kernel.org/r/20170724100428.19173-1-alexander.shishkin@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
This patch is to resolve the problem shown as follows, when testing KGDB with 'echo kgdbts=V1 > /sys/module/kgdbts/parameters/kgdbts':
[ 196.275931] Kernel panic - not syncing: Recursive entry to debugger
[ 196.276658] CPU: 0 PID: 1495 Comm: sh Not tainted 4.12.16-yocto-standard #2
[ 196.277648] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
[ 196.278634] Call Trace:
[ 196.278891] <IRQ>
[ 196.279124] dump_stack+0x65/0x8d
[ 196.279477] ? kgdb_breakpoint+0x13/0x20
[ 196.279968] kgdb_handle_exception+0x16e/0x1a0
[ 196.280405] __kgdb_notify+0x6d/0xd0
[ 196.280761] kgdb_notify+0x23/0x40
[ 196.281189] notifier_call_chain+0x4a/0x70
[ 196.281589] atomic_notifier_call_chain+0x33/0x50
[ 196.282033] notify_die+0x2e/0x30
[ 196.282469] do_int3+0x70/0x100
[ 196.282792] int3+0x35/0x70
[ 196.283080] RIP: 0010:kgdb_breakpoint+0x14/0x20
[ 196.283596] RSP: 0000:ffff9f2a0fc01d00 EFLAGS: 00000002
[ 196.284078] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: 00000000ffffffff
[ 196.284751] RDX: ffffffffa90cd700 RSI: 0000000000000000 RDI: ffffffffa8e4ca10
[ 196.285356] RBP: ffff9f2a0fc01d00 R08: 0000000000000000 R09: ffffffffa8e4ca10
[ 196.286002] R10: ffff9f2a0fc01e00 R11: ffffffffa90d40ed R12: ffffffffa8e4d2e0
[ 196.286614] R13: 0000000000000000 R14: ffffffffa90cd700 R15: 0000000000000000
Signed-off-by: Hongzhi.Song <hongzhi.song@xxxxxxxxxxxxx>
---
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);
--
2.8.1