From: Thomas Gleixner tglx@linutronix.de

stable inclusion from stable-v5.10.224 commit 19f108b3d1cafab159078a26ac93a64cab47258b category: bugfix bugzilla: 189268

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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commit f944ffcbc2e1c759764850261670586ddf3bdabb upstream.

For systems on which the performance counter can expire early due to turbo modes the watchdog handler has a safety net in place which validates that since the last watchdog event there has at least 4/5th of the watchdog period elapsed.

This works reliably only after the first watchdog event because the per CPU variable which holds the timestamp of the last event is never initialized.

So a first spurious event will validate against a timestamp of 0 which results in a delta which is likely to be way over the 4/5 threshold of the period. As this might happen before the first watchdog hrtimer event increments the watchdog counter, this can lead to false positives.

Fix this by initializing the timestamp before enabling the hardware event. Reset the rearm counter as well, as that might be non zero after the watchdog was disabled and reenabled.

Link: https://lkml.kernel.org/r/87frsfu15a.ffs@tglx Fixes: 7edaeb6841df ("kernel/watchdog: Prevent false positives with turbo modes") Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Arjan van de Ven arjan@linux.intel.com Cc: Peter Zijlstra peterz@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Conflicts: kernel/watchdog_hld.c [Fix context conflicts] Signed-off-by: Luo Gengkun luogengkun2@huawei.com --- kernel/watchdog_hld.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c index cb7053a6ba49..e4f158f56eda 100644 --- a/kernel/watchdog_hld.c +++ b/kernel/watchdog_hld.c @@ -290,11 +290,15 @@ void refresh_hld_last_timestamp(void) __this_cpu_write(last_timestamp, now);

} -#else -static inline bool watchdog_check_timestamp(void) + +static void watchdog_init_timestamp(void) { - return true; + __this_cpu_write(nmi_rearmed, 0); + __this_cpu_write(last_timestamp, ktime_get_mono_fast_ns()); } +#else +static inline bool watchdog_check_timestamp(void) { return true; } +static inline void watchdog_init_timestamp(void) { } #endif

void watchdog_hardlockup_check(struct pt_regs *regs) @@ -416,6 +420,7 @@ void hardlockup_detector_perf_enable(void) if (!atomic_fetch_inc(&watchdog_cpus)) pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");

+ watchdog_init_timestamp(); perf_event_enable(this_cpu_read(watchdog_ev)); }