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    Subject[PATCH] tracing: Fix preempt count leak
    While running my ftrace stress test, this showed up:

    BUG: sleeping function called from invalid context at mm/mmap.c:233
    ...
    note: cat[3293] exited with preempt_count 1

    The bug was introduced by commit 91e86e560d0b3ce4c5fc64fd2bbb99f856a30a4e
    ("tracing: Fix recursive user stack trace")

    Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
    ---
    kernel/trace/trace.c | 6 ++----
    1 files changed, 2 insertions(+), 4 deletions(-)

    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index c380612..5767457 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -1313,12 +1313,10 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)

    __this_cpu_inc(user_stack_count);

    -
    -
    event = trace_buffer_lock_reserve(buffer, TRACE_USER_STACK,
    sizeof(*entry), flags, pc);
    if (!event)
    - return;
    + goto out_drop_count;
    entry = ring_buffer_event_data(event);

    entry->tgid = current->tgid;
    @@ -1333,8 +1331,8 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
    if (!filter_check_discard(call, entry, buffer, event))
    ring_buffer_unlock_commit(buffer, event);

    + out_drop_count:
    __this_cpu_dec(user_stack_count);
    -
    out:
    preempt_enable();
    }
    --
    1.6.3

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