On Mon, Jul 24, 2017 at 01:04:28PM +0300, Alexander Shishkin wrote:
> 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.
So arguable it might be nice to have kgdb trap on a WARN, but it
treating it as a BUG is obviously undesirable.
Jason, what would you want kgdb to do here?
> Signed-off-by: Alexander Shishkin <[email protected]>
> Cc: Arjan van de Ven <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Richard Weinberger <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: [email protected]
> ---
> 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
>
