blktrace: fix a race when creating blk_tree_root in debugfs
t1 t2
------ ------
do_blk_trace_setup() do_blk_trace_setup()
if (!blk_tree_root) {
if (!blk_tree_root)
blk_tree_root = create_dir()
blk_tree_root = create_dir();
(now blk_tree_root == NULL)
...
dir = create_dir(name, blk_tree_root);
Due to this race, t1 will create 'dir' in /debugfs but not /debugfs/block.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index ee7a8bb..95f89fa 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -426,11 +426,15 @@
ret = -ENOENT;
+ mutex_lock(&blk_tree_mutex);
if (!blk_tree_root) {
blk_tree_root = debugfs_create_dir("block", NULL);
- if (!blk_tree_root)
+ if (!blk_tree_root) {
+ mutex_unlock(&blk_tree_mutex);
goto err;
+ }
}
+ mutex_unlock(&blk_tree_mutex);
dir = debugfs_create_dir(buts->name, blk_tree_root);