From: Alexander Shishkin alexander.shishkin@linux.intel.com

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

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@windriver.com --- 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);