[PATCH] powerpc/watchdog: Fix wd_smp_last_reset_tb reporting

[Laurent Dufour]

On 25/11/2021, 11:33:46, Nicholas Piggin wrote:
> wd_smp_last_reset_tb now gets reset by watchdog_smp_panic() as part of
> marking CPUs stuck and removing them from the pending mask before it
> begins any printing. This causes last reset times reported to be off.
> 
> Fix this by reading it into a local variable before it gets reset.
> 
> Fixes: 76521c4b0291 ("powerpc/watchdog: Avoid holding wd_smp_lock over printk and smp_send_nmi_ipi")
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> 
> This is the delta for patches 1-4 between v3 and v4 of the series which
> is the result of fixing the bug in patch 3. Sending because v3 got
> merged into powerpc next

What about the 5th patch in the v4 series titled "[PATCH v4 5/5]
powerpc/watchdog: help remote CPUs to flush NMI printk output"?


> Thanks,
> Nick
> 
>  arch/powerpc/kernel/watchdog.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
> index b6533539386b..23745af38d62 100644
> --- a/arch/powerpc/kernel/watchdog.c
> +++ b/arch/powerpc/kernel/watchdog.c
> @@ -179,13 +179,14 @@ static void watchdog_smp_panic(int cpu)
>  {
>  	static cpumask_t wd_smp_cpus_ipi; // protected by reporting
>  	unsigned long flags;
> -	u64 tb;
> +	u64 tb, last_reset;
>  	int c;
>  
>  	wd_smp_lock(&flags);
>  	/* Double check some things under lock */
>  	tb = get_tb();
> -	if ((s64)(tb - wd_smp_last_reset_tb) < (s64)wd_smp_panic_timeout_tb)
> +	last_reset = wd_smp_last_reset_tb;
> +	if ((s64)(tb - last_reset) < (s64)wd_smp_panic_timeout_tb)
>  		goto out;
>  	if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending))
>  		goto out;
> @@ -210,8 +211,7 @@ static void watchdog_smp_panic(int cpu)
>  	pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n",
>  		 cpu, cpumask_pr_args(&wd_smp_cpus_ipi));
>  	pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n",
> -		 cpu, tb, wd_smp_last_reset_tb,
> -		 tb_to_ns(tb - wd_smp_last_reset_tb) / 1000000);
> +		 cpu, tb, last_reset, tb_to_ns(tb - last_reset) / 1000000);
>  
>  	if (!sysctl_hardlockup_all_cpu_backtrace) {
>  		/*
>