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 points 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>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 9acb29f280ec95813612a913307e4dcaec8b7e03..6d1020c03d41439d298d1c219ab6dc34d1b7eda3 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -344,7 +344,6 @@ 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)