+++ /dev/null
-From 54442bdc9b81e30e6af89b1d3c5eafdc19a8c5ca Mon Sep 17 00:00:00 2001
-From: Sasha Levin <sashal@kernel.org>
-Date: Thu, 29 Apr 2021 22:54:36 -0700
-Subject: watchdog: cleanup handling of false positives
-
-From: Petr Mladek <pmladek@suse.com>
-
-[ Upstream commit 9bf3bc949f8aeefeacea4b1198db833b722a8e27 ]
-
-Commit d6ad3e286d2c ("softlockup: Add sched_clock_tick() to avoid kernel
-warning on kgdb resume") introduced touch_softlockup_watchdog_sync().
-
-It solved a problem when the watchdog was touched in an atomic context,
-the timer callback was proceed right after releasing interrupts, and the
-local clock has not been updated yet. In this case, sched_clock_tick()
-was called in watchdog_timer_fn() before updating the timer.
-
-So far so good.
-
-Later commit 5d1c0f4a80a6 ("watchdog: add check for suspended vm in
-softlockup detector") added two kvm_check_and_clear_guest_paused()
-calls. They touch the watchdog when the guest has been sleeping.
-
-The code makes my head spin around.
-
-Scenario 1:
-
- + guest did sleep:
- + PVCLOCK_GUEST_STOPPED is set
-
- + 1st watchdog_timer_fn() invocation:
- + the watchdog is not touched yet
- + is_softlockup() returns too big delay
- + kvm_check_and_clear_guest_paused():
- + clear PVCLOCK_GUEST_STOPPED
- + call touch_softlockup_watchdog_sync()
- + set SOFTLOCKUP_DELAY_REPORT
- + set softlockup_touch_sync
- + return from the timer callback
-
- + 2nd watchdog_timer_fn() invocation:
-
- + call sched_clock_tick() even though it is not needed.
- The timer callback was invoked again only because the clock
- has already been updated in the meantime.
-
- + call kvm_check_and_clear_guest_paused() that does nothing
- because PVCLOCK_GUEST_STOPPED has been cleared already.
-
- + call update_report_ts() and return. This is fine. Except
- that sched_clock_tick() might allow to set it already
- during the 1st invocation.
-
-Scenario 2:
-
- + guest did sleep
-
- + 1st watchdog_timer_fn() invocation
- + same as in 1st scenario
-
- + guest did sleep again:
- + set PVCLOCK_GUEST_STOPPED again
-
- + 2nd watchdog_timer_fn() invocation
- + SOFTLOCKUP_DELAY_REPORT is set from 1st invocation
- + call sched_clock_tick()
- + call kvm_check_and_clear_guest_paused()
- + clear PVCLOCK_GUEST_STOPPED
- + call touch_softlockup_watchdog_sync()
- + set SOFTLOCKUP_DELAY_REPORT
- + set softlockup_touch_sync
- + call update_report_ts() (set real timestamp immediately)
- + return from the timer callback
-
- + 3rd watchdog_timer_fn() invocation
- + timestamp is set from 2nd invocation
- + softlockup_touch_sync is set but not checked because
- the real timestamp is already set
-
-Make the code more straightforward:
-
-1. Always call kvm_check_and_clear_guest_paused() at the very
- beginning to handle PVCLOCK_GUEST_STOPPED. It touches the watchdog
- when the quest did sleep.
-
-2. Handle the situation when the watchdog has been touched
- (SOFTLOCKUP_DELAY_REPORT is set).
-
- Call sched_clock_tick() when touch_*sync() variant was used. It makes
- sure that the timestamp will be up to date even when it has been
- touched in atomic context or quest did sleep.
-
-As a result, kvm_check_and_clear_guest_paused() is called on a single
-location. And the right timestamp is always set when returning from the
-timer callback.
-
-Link: https://lkml.kernel.org/r/20210311122130.6788-7-pmladek@suse.com
-Signed-off-by: Petr Mladek <pmladek@suse.com>
-Cc: Ingo Molnar <mingo@kernel.org>
-Cc: Laurence Oberman <loberman@redhat.com>
-Cc: Michal Hocko <mhocko@suse.com>
-Cc: Peter Zijlstra <peterz@infradead.org>
-Cc: Thomas Gleixner <tglx@linutronix.de>
-Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
-Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-Signed-off-by: Sasha Levin <sashal@kernel.org>
----
- kernel/watchdog.c | 20 ++++++++------------
- 1 file changed, 8 insertions(+), 12 deletions(-)
-
-diff --git a/kernel/watchdog.c b/kernel/watchdog.c
-index 8cf0678378d2..7c397907d0e9 100644
---- a/kernel/watchdog.c
-+++ b/kernel/watchdog.c
-@@ -376,7 +376,14 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
- /* .. and repeat */
- hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
-
-- /* Reset the interval when touched externally by a known slow code. */
-+ /*
-+ * If a virtual machine is stopped by the host it can look to
-+ * the watchdog like a soft lockup. Check to see if the host
-+ * stopped the vm before we process the timestamps.
-+ */
-+ kvm_check_and_clear_guest_paused();
-+
-+ /* Reset the interval when touched by known problematic code. */
- if (period_ts == SOFTLOCKUP_DELAY_REPORT) {
- if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
- /*
-@@ -387,10 +394,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
- sched_clock_tick();
- }
-
-- /* Clear the guest paused flag on watchdog reset */
-- kvm_check_and_clear_guest_paused();
- update_report_ts();
--
- return HRTIMER_RESTART;
- }
-
-@@ -402,14 +406,6 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
- */
- duration = is_softlockup(touch_ts, period_ts);
- if (unlikely(duration)) {
-- /*
-- * If a virtual machine is stopped by the host it can look to
-- * the watchdog like a soft lockup, check to see if the host
-- * stopped the vm before we issue the warning
-- */
-- if (kvm_check_and_clear_guest_paused())
-- return HRTIMER_RESTART;
--
- /*
- * Prevent multiple soft-lockup reports if one cpu is already
- * engaged in dumping all cpu back traces.
---
-2.30.2
-
projects / thirdparty / kernel / stable-queue.git / commitdiff
