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powerpc/crash: stop watchdogs before booting kdump kernel

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On pseries LPAR systems, watchdog timers configured from userspace can
remain active after a kernel panic. When a panic triggers kdump, the
crashing kernel jumps directly to the kdump kernel without stopping
active watchdogs. As a result, the watchdogs remain active after the
kdump kernel starts.

If dump capture takes longer than the watchdog timeout, PHYP resets the
LPAR before the dump is fully captured, causing dump capture to fail.

Fix this by issuing the `H_WATCHDOG` hcall during the crash shutdown
sequence to stop all active watchdogs before booting the kdump kernel.

Cc: stable@vger.kernel.org
Fixes: 69472ffa65 ("watchdog/pseries-wdt: initial support for H_WATCHDOG-based watchdog timers")
Reported-by: Mahesh Kumar G <mahe657@linux.ibm.com>
Suggested-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260727053416.276317-4-sourabhjain@linux.ibm.com
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Sourabh Jain 2026-07-27 11:04:16 +05:30 • committed by Madhavan Srinivasan
commit fb43ba4256
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