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    Subject[PATCH 5.9 278/757] coresight: etm4x: Handle unreachable sink in perf mode
    Date
    From: Suzuki K Poulose <suzuki.poulose@arm.com>

    [ Upstream commit 859d510e58dac94f0b204b7b5cccafbc130d2291 ]

    If the specified/hinted sink is not reachable from a subset of the CPUs,
    we could end up unable to trace the event on those CPUs. This
    is the best effort we could do until we support 1:1 configurations.
    Fail gracefully in such cases avoiding a WARN_ON, which can be easily
    triggered by the user on certain platforms (Arm N1SDP), with the following
    trace paths :

    CPU0
    \
    -- Funnel0 --> ETF0 -->
    / \
    CPU1 \
    MainFunnel
    CPU2 /
    \ /
    -- Funnel1 --> ETF1 -->
    /
    CPU1

    $ perf record --per-thread -e cs_etm/@ETF0/u -- <app>

    could trigger the following WARNING, when the event is scheduled
    on CPU2.

    [10919.513250] ------------[ cut here ]------------
    [10919.517861] WARNING: CPU: 2 PID: 24021 at
    drivers/hwtracing/coresight/coresight-etm-perf.c:316 etm_event_start+0xf8/0x100
    ...

    [10919.564403] CPU: 2 PID: 24021 Comm: perf Not tainted 5.8.0+ #24
    [10919.570308] pstate: 80400089 (Nzcv daIf +PAN -UAO BTYPE=--)
    [10919.575865] pc : etm_event_start+0xf8/0x100
    [10919.580034] lr : etm_event_start+0x80/0x100
    [10919.584202] sp : fffffe001932f940
    [10919.587502] x29: fffffe001932f940 x28: fffffc834995f800
    [10919.592799] x27: 0000000000000000 x26: fffffe0011f3ced0
    [10919.598095] x25: fffffc837fce244c x24: fffffc837fce2448
    [10919.603391] x23: 0000000000000002 x22: fffffc8353529c00
    [10919.608688] x21: fffffc835bb31000 x20: 0000000000000000
    [10919.613984] x19: fffffc837fcdcc70 x18: 0000000000000000
    [10919.619281] x17: 0000000000000000 x16: 0000000000000000
    [10919.624577] x15: 0000000000000000 x14: 00000000000009f8
    [10919.629874] x13: 00000000000009f8 x12: 0000000000000018
    [10919.635170] x11: 0000000000000000 x10: 0000000000000000
    [10919.640467] x9 : fffffe00108cd168 x8 : 0000000000000000
    [10919.645763] x7 : 0000000000000020 x6 : 0000000000000001
    [10919.651059] x5 : 0000000000000002 x4 : 0000000000000001
    [10919.656356] x3 : 0000000000000000 x2 : 0000000000000000
    [10919.661652] x1 : fffffe836eb40000 x0 : 0000000000000000
    [10919.666949] Call trace:
    [10919.669382] etm_event_start+0xf8/0x100
    [10919.673203] etm_event_add+0x40/0x60
    [10919.676765] event_sched_in.isra.134+0xcc/0x210
    [10919.681281] merge_sched_in+0xb0/0x2a8
    [10919.685017] visit_groups_merge.constprop.140+0x15c/0x4b8
    [10919.690400] ctx_sched_in+0x15c/0x170
    [10919.694048] perf_event_sched_in+0x6c/0xa0
    [10919.698130] ctx_resched+0x60/0xa0
    [10919.701517] perf_event_exec+0x288/0x2f0
    [10919.705425] begin_new_exec+0x4c8/0xf58
    [10919.709247] load_elf_binary+0x66c/0xf30
    [10919.713155] exec_binprm+0x15c/0x450
    [10919.716716] __do_execve_file+0x508/0x748
    [10919.720711] __arm64_sys_execve+0x40/0x50
    [10919.724707] do_el0_svc+0xf4/0x1b8
    [10919.728095] el0_sync_handler+0xf8/0x124
    [10919.732003] el0_sync+0x140/0x180

    Even though we don't support using separate sinks for the ETMs yet (e.g,
    for 1:1 configurations), we should at least honor the user's choice and
    handle the limitations gracefully, by simply skipping the tracing on ETMs
    which can't reach the requested sink.

    Fixes: f9d81a657bb8 ("coresight: perf: Allow tracing on hotplugged CPUs")
    Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
    Cc: Mike Leach <mike.leach@linaro.org>
    Reported-by: Jeremy Linton <jeremy.linton@arm.com>
    Tested-by: Jeremy Linton <jeremy.linton@arm.com>
    Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
    Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
    Link: https://lore.kernel.org/r/20200916191737.4001561-11-mathieu.poirier@linaro.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/hwtracing/coresight/coresight-etm-perf.c | 10 ++++++++++
    1 file changed, 10 insertions(+)

    diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
    index 1a3169e69bb19..9d61a71da96f7 100644
    --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
    +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
    @@ -321,6 +321,16 @@ static void etm_event_start(struct perf_event *event, int flags)
    if (!event_data)
    goto fail;

    + /*
    + * Check if this ETM is allowed to trace, as decided
    + * at etm_setup_aux(). This could be due to an unreachable
    + * sink from this ETM. We can't do much in this case if
    + * the sink was specified or hinted to the driver. For
    + * now, simply don't record anything on this ETM.
    + */
    + if (!cpumask_test_cpu(cpu, &event_data->mask))
    + goto fail_end_stop;
    +
    path = etm_event_cpu_path(event_data, cpu);
    /* We need a sink, no need to continue without one */
    sink = coresight_get_sink(path);
    --
    2.25.1


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