Commit bcfba4f4 authored by Ulrich Obergfell's avatar Ulrich Obergfell Committed by Linus Torvalds
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watchdog: implement error handling for failure to set up hardware perf events

If watchdog_nmi_enable() fails to set up the hardware perf event of one
CPU, the entire hard lockup detector is deemed unreliable.  Hence, disable
the hard lockup detector and shut down the hardware perf events on all

[ update comments to explain some code]
Signed-off-by: default avatarUlrich Obergfell <>
Signed-off-by: default avatarDon Zickus <>
Cc: Ingo Molnar <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 83a80a39
......@@ -502,6 +502,21 @@ static void watchdog(unsigned int cpu)
* watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
* failure path. Check for failures that can occur asynchronously -
* for example, when CPUs are on-lined - and shut down the hardware
* perf event on each CPU accordingly.
* The only non-obvious place this bit can be cleared is through
* watchdog_nmi_enable(), so a pr_info() is placed there. Placing a
* pr_info here would be too noisy as it would result in a message
* every few seconds if the hardlockup was disabled but the softlockup
* enabled.
if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
......@@ -552,6 +567,18 @@ static int watchdog_nmi_enable(unsigned int cpu)
goto out_save;
* Disable the hard lockup detector if _any_ CPU fails to set up
* set up the hardware perf event. The watchdog() function checks
* the NMI_WATCHDOG_ENABLED bit periodically.
* The barriers are for syncing up watchdog_enabled across all the
* cpus, as clear_bit() does not use barriers.
clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
/* skip displaying the same error again */
if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
return PTR_ERR(event);
......@@ -565,6 +592,9 @@ static int watchdog_nmi_enable(unsigned int cpu)
pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
cpu, PTR_ERR(event));
pr_info("Shutting down hard lockup detector on all cpus\n");
return PTR_ERR(event);
/* success path */
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