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    SubjectRe: [PATCH 3/7] blktrace: remove blk_probe_mutex
    On Fri, Mar 20, 2009 at 09:48:26AM +0800, Li Zefan wrote:
    > blk_register_tracepoints() always returns 0, so make it return void, thus
    > we don't need to use blk_probe_mutex to protect blk_probes_ref.
    >
    > Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
    > ---
    > kernel/trace/blktrace.c | 27 +++++----------------------
    > 1 files changed, 5 insertions(+), 22 deletions(-)
    >
    > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
    > index 73845b7..223b92e 100644
    > --- a/kernel/trace/blktrace.c
    > +++ b/kernel/trace/blktrace.c
    > @@ -47,10 +47,9 @@ static struct tracer_flags blk_tracer_flags = {
    > };
    >
    > /* Global reference count of probes */
    > -static DEFINE_MUTEX(blk_probe_mutex);
    > static atomic_t blk_probes_ref = ATOMIC_INIT(0);
    >
    > -static int blk_register_tracepoints(void);
    > +static void blk_register_tracepoints(void);
    > static void blk_unregister_tracepoints(void);
    >
    > /*
    > @@ -256,10 +255,8 @@ static void blk_trace_cleanup(struct blk_trace *bt)
    > free_percpu(bt->sequence);
    > free_percpu(bt->msg_data);
    > kfree(bt);
    > - mutex_lock(&blk_probe_mutex);
    > if (atomic_dec_and_test(&blk_probes_ref))
    > blk_unregister_tracepoints();
    > - mutex_unlock(&blk_probe_mutex);
    > }
    >
    > int blk_trace_remove(struct request_queue *q)
    > @@ -471,13 +468,8 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
    > bt->pid = buts->pid;
    > bt->trace_state = Blktrace_setup;
    >
    > - mutex_lock(&blk_probe_mutex);
    > - if (atomic_add_return(1, &blk_probes_ref) == 1) {
    > - ret = blk_register_tracepoints();
    > - if (ret)
    > - goto probe_err;
    > - }
    > - mutex_unlock(&blk_probe_mutex);
    > + if (atomic_add_return(1, &blk_probes_ref) == 1)


    atomic_inc_return() is a bit more simple.


    > + blk_register_tracepoints();
    >
    > ret = -EBUSY;
    > old_bt = xchg(&q->blk_trace, bt);
    > @@ -487,9 +479,6 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
    > }
    >
    > return 0;
    > -probe_err:
    > - atomic_dec(&blk_probes_ref);
    > - mutex_unlock(&blk_probe_mutex);
    > err:
    > if (bt) {
    > if (bt->msg_file)
    > @@ -863,7 +852,7 @@ void blk_add_driver_data(struct request_queue *q,
    > }
    > EXPORT_SYMBOL_GPL(blk_add_driver_data);
    >
    > -static int blk_register_tracepoints(void)
    > +static void blk_register_tracepoints(void)
    > {
    > int ret;
    >
    > @@ -901,7 +890,6 @@ static int blk_register_tracepoints(void)
    > WARN_ON(ret);
    > ret = register_trace_block_remap(blk_add_trace_remap);
    > WARN_ON(ret);
    > - return 0;
    > }
    >
    > static void blk_unregister_tracepoints(void)
    > @@ -1099,11 +1087,8 @@ static void blk_tracer_print_header(struct seq_file *m)
    >
    > static void blk_tracer_start(struct trace_array *tr)
    > {
    > - mutex_lock(&blk_probe_mutex);
    > if (atomic_add_return(1, &blk_probes_ref) == 1)
    > - if (blk_register_tracepoints())
    > - atomic_dec(&blk_probes_ref);
    > - mutex_unlock(&blk_probe_mutex);
    > + blk_register_tracepoints();
    > trace_flags &= ~TRACE_ITER_CONTEXT_INFO;
    > }
    >
    > @@ -1118,10 +1103,8 @@ static int blk_tracer_init(struct trace_array *tr)
    > static void blk_tracer_stop(struct trace_array *tr)
    > {
    > trace_flags |= TRACE_ITER_CONTEXT_INFO;
    > - mutex_lock(&blk_probe_mutex);
    > if (atomic_dec_and_test(&blk_probes_ref))
    > blk_unregister_tracepoints();
    > - mutex_unlock(&blk_probe_mutex);
    > }
    >
    > static void blk_tracer_reset(struct trace_array *tr)
    > --
    > 1.5.4.rc3
    >

    Looks good.



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