kernel/watchdog: use nmi registers snapshot in hardlockup handler

commit 4d1f0fb096aedea7bb5489af93498a82e467c480 upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 198137b1cadc6a8438cf105270c0229ccc4149e5..c1e0b5f429b6b91c9b80c0173f8c8668541fbde8 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -328,7 +328,6 @@ 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)