blktrace: use existing disk debugfs directory

We may already have a directory to put the blktrace stuff in if

1. The disk uses blk-mq
2. CONFIG_BLK_DEBUG_FS is enabled
3. We are tracing the whole disk and not a partition

Instead of hardcoding this very specific case, let's use the new
debugfs_lookup(). If the directory exists, we use it, otherwise we
create one and clean it up later.

Fixes: 07e4fead45e6 ("blk-mq: create debugfs directory tree")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 8cea91d..b2058a7 100644 (file)
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -470,12 +470,12 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
        if (!blk_debugfs_root)
                goto err;
 
-       dir = debugfs_create_dir(buts->name, blk_debugfs_root);
-
+       dir = debugfs_lookup(buts->name, blk_debugfs_root);
+       if (!dir)
+               bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root);
        if (!dir)
                goto err;
 
-       bt->dir = dir;
        bt->dev = dev;
        atomic_set(&bt->dropped, 0);
        INIT_LIST_HEAD(&bt->running_list);
@@ -517,9 +517,12 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
        if (atomic_inc_return(&blk_probes_ref) == 1)
                blk_register_tracepoints();
 
-       return 0;
+       ret = 0;
 err:
-       blk_trace_free(bt);
+       if (dir && !bt->dir)
+               dput(dir);
+       if (ret)
+               blk_trace_free(bt);
        return ret;
 }