[linux-yocto] [yocto-4.12] [PATCH] x86/debug: Handle warnings before the notifier chain, to fix KGDB crash
Bruce Ashfield
bruce.ashfield at windriver.com
Mon Dec 18 14:00:42 PST 2017
staged.
Once build/boot testing completes, I'll send SRCREV updates.
Bruce
On 2017-12-14 1:52 AM, Hongzhi.Song wrote:
> From: Alexander Shishkin <alexander.shishkin at 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 at linux.intel.com>
> Tested-by: Ilya Dryomov <idryomov at gmail.com>
> Acked-by: Daniel Thompson <daniel.thompson at linaro.org>
> Acked-by: Thomas Gleixner <tglx at linutronix.de>
> Cc: Jason Wessel <jason.wessel at windriver.com>
> Cc: Arjan van de Ven <arjan at linux.intel.com>
> Cc: Borislav Petkov <bp at alien8.de>
> Cc: Linus Torvalds <torvalds at linux-foundation.org>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Richard Weinberger <richard.weinberger at gmail.com>
> Cc: <stable at 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 at 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 at 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);
>
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