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| H A D | time.c | diff abc3fce76adbdfa8f87272c784b388cd20b46049 Thu Apr 02 07:04:01 CDT 2020 Nicholas Piggin <npiggin@gmail.com> Revert "powerpc/64: irq_work avoid interrupt when called with hardware irqs enabled"
This reverts commit ebb37cf3ffd39fdb6ec5b07111f8bb2f11d92c5f.
That commit does not play well with soft-masked irq state
manipulations in idle, interrupt replay, and possibly others due to
tracing code sometimes using irq_work_queue (e.g., in
trace_hardirqs_on()). That can cause PACA_IRQ_DEC to become set when
it is not expected, and be ignored or cleared or cause warnings.
The net result seems to be missing an irq_work until the next timer
interrupt in the worst case which is usually not going to be noticed,
however it could be a long time if the tick is disabled, which is
against the spirit of irq_work and might cause real problems.
The idea is still solid, but it would need more work. It's not really
clear if it would be worth added complexity, so revert this for
now (not a straight revert, but replace with a comment explaining why
we might see interrupts happening, and gives git blame something to
find).
Fixes: ebb37cf3ffd3 ("powerpc/64: irq_work avoid interrupt when called with hardware irqs enabled")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200402120401.1115883-1-npiggin@gmail.com
diff ebb37cf3ffd39fdb6ec5b07111f8bb2f11d92c5f Fri May 04 12:19:25 CDT 2018 Nicholas Piggin <npiggin@gmail.com> powerpc/64: irq_work avoid interrupt when called with hardware irqs enabled
irq_work_raise should not cause a decrementer exception unless it is
called from NMI context. Doing so often just results in an immediate
masked decrementer interrupt:
<...>-550 90d... 4us : update_curr_rt <-dequeue_task_rt
<...>-550 90d... 5us : dbs_update_util_handler <-update_curr_rt
<...>-550 90d... 6us : arch_irq_work_raise <-irq_work_queue
<...>-550 90d... 7us : soft_nmi_interrupt <-soft_nmi_common
<...>-550 90d... 7us : printk_nmi_enter <-soft_nmi_interrupt
<...>-550 90d.Z. 8us : rcu_nmi_enter <-soft_nmi_interrupt
<...>-550 90d.Z. 9us : rcu_nmi_exit <-soft_nmi_interrupt
<...>-550 90d... 9us : printk_nmi_exit <-soft_nmi_interrupt
<...>-550 90d... 10us : cpuacct_charge <-update_curr_rt
The soft_nmi_interrupt here is the call into the watchdog, due to the
decrementer interrupt firing with irqs soft-disabled. This is
harmless, but sub-optimal.
When it's not called from NMI context or with interrupts enabled, mark
the decrementer pending in the irq_happened mask directly, rather than
having the masked decrementer interupt handler do it. This will be
replayed at the next local_irq_enable. See the comment for details.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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