Attachment 1750515 Details for Bug 1916589 – RHEL PATCH 1/1

RHEL PATCH 1/1

0001-kernel-watchdog-use-nmi-registers-snapshot-in-hardlo.patch (text/plain), 2.50 KB, created by Prarit Bhargava on 2021-01-25 13:33:46 UTC

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Creator: Prarit Bhargava

Created: 2021-01-25 13:33:46 UTC

Size: 2.50 KB

patch

obsolete

>From aadb965b8c7bfed32ab24fc3c6ebbdb1d53531ec Mon Sep 17 00:00:00 2001
>From: Prarit Bhargava <prarit@redhat.com>
>Date: Fri, 15 Jan 2021 08:39:55 -0500
>Subject: [PATCH] kernel/watchdog: use nmi registers snapshot in hardlockup
> handler
>
>Bugzilla: http://bugzilla.redhat.com/1916589
>
>This line was introduced in RHEL7 commit b7557e36b465 ("[kernel] watchdog:
>perform all-CPU backtrace in case of hard lockup") and causes a regression
>during panic where the regs are missing.  As a result it is not possible
>to debug in kdump.
>
>Tested: I've tried to reproduce locally, however, it appears
>the the problem has low reproducibility.  I have sanity tested this patch
>and confirmed that kdump does work in RHEL7.
>
>commit 4d1f0fb096aedea7bb5489af93498a82e467c480
>Author: Konstantin Khlebnikov <koct9i@gmail.com>
>Date:   Wed Dec 14 15:04:04 2016 -0800
>
>    kernel/watchdog: use nmi registers snapshot in hardlockup handler
>
>    NMI handler doesn't call set_irq_regs(), it's set only by normal IRQ.
>    Thus get_irq_regs() returns NULL or stale registers snapshot with IP/SP
>    pointing to the code interrupted by IRQ which was interrupted by NMI.
>    NULL isn't a problem: in this case watchdog calls dump_stack() and
>    prints full stack trace including NMI.  But if we're stuck in IRQ
>    handler then NMI watchlog will print stack trace without IRQ part at
>    all.
>
>    This patch uses registers snapshot passed into NMI handler as arguments:
>    these registers point exactly to the instruction interrupted by NMI.
>
>    Fixes: 55537871ef66 ("kernel/watchdog.c: perform all-CPU backtrace in case of hard lockup")
>    Link: http://lkml.kernel.org/r/146771764784.86724.6006627197118544150.stgit@buzz
>    Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>    Cc: Jiri Kosina <jkosina@suse.cz>
>    Cc: Ulrich Obergfell <uobergfe@redhat.com>
>    Cc: Aaron Tomlin <atomlin@redhat.com>
>    Cc: <stable@vger.kernel.org>    [4.4+]
>    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
>---
> kernel/watchdog.c | 1 -
> 1 file changed, 1 deletion(-)
>
>diff --git a/kernel/watchdog.c b/kernel/watchdog.c
>index 669e77678318..a72e2aa21100 100644
>--- a/kernel/watchdog.c
>+++ b/kernel/watchdog.c
>@@ -414,7 +414,6 @@ static void watchdog_overflow_callback(struct perf_event *event,
> 	 */
> 	if (is_hardlockup()) {
> 		int this_cpu = smp_processor_id();
>-		struct pt_regs *regs = get_irq_regs();
> 
> 		/* only print hardlockups once */
> 		if (__this_cpu_read(hard_watchdog_warn) == true)
>-- 
>2.29.2
>

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