Commit 757d9140 authored Aug 16, 2018 by Steven Rostedt (VMware) Committed by Jens Axboe Aug 16, 2018

tracing/blktrace: Fix to allow setting same value

Masami Hiramatsu reported:

  Current trace-enable attribute in sysfs returns an error
  if user writes the same setting value as current one,
  e.g.

    # cat /sys/block/sda/trace/enable
    0
    # echo 0 > /sys/block/sda/trace/enable
    bash: echo: write error: Invalid argument
    # echo 1 > /sys/block/sda/trace/enable
    # echo 1 > /sys/block/sda/trace/enable
    bash: echo: write error: Device or resource busy

  But this is not a preferred behavior, it should ignore
  if new setting is same as current one. This fixes the
  problem as below.

    # cat /sys/block/sda/trace/enable
    0
    # echo 0 > /sys/block/sda/trace/enable
    # echo 1 > /sys/block/sda/trace/enable
    # echo 1 > /sys/block/sda/trace/enable

Link: http://lkml.kernel.org/r/20180816103802.08678002@gandalf.local.home



Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: cd649b8b ("blktrace: remove sysfs_blk_trace_enable_show/store()")
Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 566484a9

kernel/trace/blktrace.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -1841,6 +1841,10 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
		mutex_lock(&q->blk_trace_mutex);

		if (attr == &dev_attr_enable) {
		if (!!value == !!q->blk_trace) {
		ret = 0;
		goto out_unlock_bdev;
		}
		if (value)
		ret = blk_trace_setup_queue(q, bdev);
		else

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