From cbde057aa0e7b2fcca06e7f6ba28b8d76a041ce9 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Thu, 16 Aug 2018 16:08:37 -0400 Subject: [PATCH] tracing/blktrace: Fix to allow setting same value 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 Cc: Jens Axboe Cc: linux-block@vger.kernel.org Cc: stable@vger.kernel.org Fixes: cd649b8bb830d ("blktrace: remove sysfs_blk_trace_enable_show/store()") Reported-by: Masami Hiramatsu Tested-by: Masami Hiramatsu Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- kernel/trace/blktrace.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index e73dcab8e9f0..71a8ee6e60dc 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -1809,6 +1809,10 @@ 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 -- 2.20.1