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    Subject[PATCH 5.4 75/85] perf: Fix task_function_call() error handling
    Date
    From: Kajol Jain <kjain@linux.ibm.com>

    [ Upstream commit 6d6b8b9f4fceab7266ca03d194f60ec72bd4b654 ]

    The error handling introduced by commit:

    2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")

    looses any return value from smp_call_function_single() that is not
    {0, -EINVAL}. This is a problem because it will return -EXNIO when the
    target CPU is offline. Worse, in that case it'll turn into an infinite
    loop.

    Fixes: 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")
    Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Reviewed-by: Barret Rhoden <brho@google.com>
    Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Link: https://lkml.kernel.org/r/20200827064732.20860-1-kjain@linux.ibm.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/events/core.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index 47646050efa0c..09e1cc22221fe 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -97,7 +97,7 @@ static void remote_function(void *data)
    * retry due to any failures in smp_call_function_single(), such as if the
    * task_cpu() goes offline concurrently.
    *
    - * returns @func return value or -ESRCH when the process isn't running
    + * returns @func return value or -ESRCH or -ENXIO when the process isn't running
    */
    static int
    task_function_call(struct task_struct *p, remote_function_f func, void *info)
    @@ -113,7 +113,8 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info)
    for (;;) {
    ret = smp_call_function_single(task_cpu(p), remote_function,
    &data, 1);
    - ret = !ret ? data.ret : -EAGAIN;
    + if (!ret)
    + ret = data.ret;

    if (ret != -EAGAIN)
    break;
    --
    2.25.1


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