4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: linux-block@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Fixes: cd649b8bb830d ("blktrace: remove sysfs_blk_trace_enable_show/store()")
Reported-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Tested-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/blktrace.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1720,6 +1720,10 @@ 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
