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powerpc/64s/interrupt: Fix decrementer storm

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The decrementer exception can fail to be cleared when the interrupt
returns in the case where the decrementer wraps with the next timer
still beyond decrementer_max. This results in a decrementer interrupt
storm. This is triggerable with small decrementer system with hard
and soft watchdogs disabled.

Fix this by always programming the decrementer if there was no timer.

Fixes: 0faf20a1ad ("powerpc/64s/interrupt: Don't enable MSR[EE] in irq handlers unless perf is in use")
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220124143930.3923442-1-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2022-01-25 00:39:28 +10:00 committed by Michael Ellerman
parent 22f7ff0dea
commit 8defc2a5dd
1 changed files with 3 additions and 2 deletions
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5
arch/powerpc/kernel/time.c
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@ -649,8 +649,9 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt)
__this_cpu_inc(irq_stat.timer_irqs_event);
} else {
now = *next_tb - now;
if (now <= decrementer_max)
set_dec_or_work(now);
if (now > decrementer_max)
now = decrementer_max;
set_dec_or_work(now);
__this_cpu_inc(irq_stat.timer_irqs_others);
}