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Date: Fri, 7 Sep 2018 23:10:32 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, "Steven Rostedt (VMware)" <rostedt@...dmis.org> Subject: [PATCH 3.18 11/29] tracing/blktrace: Fix to allow setting same value 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steven Rostedt (VMware) <rostedt@...dmis.org> commit 757d9140072054528b13bbe291583d9823cde195 upstream. 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@...hat.com> Cc: Jens Axboe <axboe@...nel.dk> Cc: linux-block@...r.kernel.org Cc: stable@...r.kernel.org Fixes: cd649b8bb830d ("blktrace: remove sysfs_blk_trace_enable_show/store()") Reported-by: Masami Hiramatsu <mhiramat@...nel.org> Tested-by: Masami Hiramatsu <mhiramat@...nel.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org> Signed-off-by: Jens Axboe <axboe@...nel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- kernel/trace/blktrace.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -1734,6 +1734,10 @@ static ssize_t sysfs_blk_trace_attr_stor mutex_lock(&bdev->bd_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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