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    Subject[PATCH 5.4 146/214] powerpc/perf: Fix soft lockups due to missed interrupt accounting
    Date
    From: Athira Rajeev <atrajeev@linux.vnet.ibm.com>

    [ Upstream commit 17899eaf88d689529b866371344c8f269ba79b5f ]

    Performance monitor interrupt handler checks if any counter has
    overflown and calls record_and_restart() in core-book3s which invokes
    perf_event_overflow() to record the sample information. Apart from
    creating sample, perf_event_overflow() also does the interrupt and
    period checks via perf_event_account_interrupt().

    Currently we record information only if the SIAR (Sampled Instruction
    Address Register) valid bit is set (using siar_valid() check) and
    hence the interrupt check.

    But it is possible that we do sampling for some events that are not
    generating valid SIAR, and hence there is no chance to disable the
    event if interrupts are more than max_samples_per_tick. This leads to
    soft lockup.

    Fix this by adding perf_event_account_interrupt() in the invalid SIAR
    code path for a sampling event. ie if SIAR is invalid, just do
    interrupt check and don't record the sample information.

    Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
    Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
    Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/1596717992-7321-1-git-send-email-atrajeev@linux.vnet.ibm.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/powerpc/perf/core-book3s.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
    index ca92e01d0bd1b..e32f7700303bc 100644
    --- a/arch/powerpc/perf/core-book3s.c
    +++ b/arch/powerpc/perf/core-book3s.c
    @@ -2106,6 +2106,10 @@ static void record_and_restart(struct perf_event *event, unsigned long val,

    if (perf_event_overflow(event, &data, regs))
    power_pmu_stop(event, 0);
    + } else if (period) {
    + /* Account for interrupt in case of invalid SIAR */
    + if (perf_event_account_interrupt(event))
    + power_pmu_stop(event, 0);
    }
    }

    --
    2.25.1


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