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    Subject[PATCH 1/2] [PATCH 1/2] ring-buffer: Synchronize resizing buffer with reader lock
    From: Lai Jiangshan <laijs@cn.fujitsu.com>

    We got a sudden panic when we reduced the size of the
    ringbuffer.

    We can reproduce the panic by the following steps:

    echo 1 > events/sched/enable
    cat trace_pipe > /dev/null &

    while ((1))
    do
    echo 12000 > buffer_size_kb
    echo 512 > buffer_size_kb
    done

    (not more than 5 seconds, panic ...)

    Reported-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    LKML-Reference: <4AF01735.9060409@cn.fujitsu.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    kernel/trace/ring_buffer.c | 2 ++
    1 files changed, 2 insertions(+), 0 deletions(-)

    diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
    index 3ffa502..5dd017f 100644
    --- a/kernel/trace/ring_buffer.c
    +++ b/kernel/trace/ring_buffer.c
    @@ -1193,6 +1193,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
    atomic_inc(&cpu_buffer->record_disabled);
    synchronize_sched();

    + spin_lock_irq(&cpu_buffer->reader_lock);
    rb_head_page_deactivate(cpu_buffer);

    for (i = 0; i < nr_pages; i++) {
    @@ -1207,6 +1208,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
    return;

    rb_reset_cpu(cpu_buffer);
    + spin_unlock_irq(&cpu_buffer->reader_lock);

    rb_check_pages(cpu_buffer);

    --
    1.6.3.3



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