Commit 489196f3 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Luo Gengkun
Browse files

watchdog/perf: properly initialize the turbo mode timestamp and rearm counter 

stable inclusion
from stable-v5.10.224
commit 19f108b3d1cafab159078a26ac93a64cab47258b
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBBONJ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=19f108b3d1cafab159078a26ac93a64cab47258b

--------------------------------

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: 7edaeb68 ("kernel/watchdog: Prevent false positives with turbo modes")
Signed-off-by: default avatarThomas 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Conflicts:
	kernel/watchdog_hld.c
[Fix context conflicts]
Signed-off-by: default avatarLuo Gengkun <luogengkun2@huawei.com>
parent dd14d8eb

kernel/watchdog_hld.c

+8 −3
Original line number Diff line number Diff line
@@ -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));

}