On 4/11/26 2:40 pm, Luiz Capitulino (Red Hat) wrote:
On powerpc, trying to disable the hardlockup detector with:
# echo 0 > /proc/sys/kernel/watchdog_thresh
causes an immediate and endless hardlockup detection, eventually leading
to an unusable system (splat example below).
...
This condition is already checked in __lockup_detector_reconfigure() for
the soft lockup detector and the arch-independent hardlockup detector,
what's missing is powerpc performing the same check in start_watchdog().
Arguably setting watchdog_thresh to 0 should mean watchdog_enabled becomes
false.
Then there wouldn't need to be extra checks for thresh == 0 anywhere.
But if the existing code already checks for thresh == 0 then this is fine.
Fixes: 2104180a5369 ("powerpc/64s: implement arch-specific hardlockup watchdog")
Cc: [email protected]
Signed-off-by: Luiz Capitulino (Red Hat) <[email protected]>
---
Notes:
- This issue was not discovered by AI. We have a new test-case in our CI that
sets watchdog_thresh=0, when running on powerpc we get the described issue
- This issue was initially reproduced on Power10, but I developed the fix
on Power9 (which is what I have access now)
arch/powerpc/kernel/watchdog.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index 582ee3fd71c1..44f178e07531 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -487,6 +487,9 @@ static void start_watchdog(void *arg)
if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED))
return;
+ if (!watchdog_thresh)
+ return;
+
if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
return;
Fix looks good to me.
Reviewed-by: Michael Ellerman <[email protected]>
cheers
