blktrace: fix a race when creating blk_tree_root in debugfs
authorLi Zefan <lizf@cn.fujitsu.com>
Wed, 25 Mar 2009 09:19:33 +0000 (17:19 +0800)
committerIngo Molnar <mingo@elte.hu>
Tue, 31 Mar 2009 15:26:59 +0000 (17:26 +0200)
commitb5230b56ee6caeb27cedb7753c0c319646383bb4
treea8cb9730ba9d89346d3bd959393e72c84b36ce84
parent6c051ce0307526adec32a847f0daa1af2124f0a9
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>
kernel/trace/blktrace.c