So, upon updating the commit log, and moving the empty directory check
into another patch, I realized we might be able to simplify this now even
further still. Patch below. The key of the issue was that the use after free
happens when a recursive removal happens, and then later a specific
dentry removal happens. This happened for make_request block drivers
when using the whole disk, but since we *don't* have any other users of
the directory for the others cases, this in theory shuld not happen for
them either.
I'll try to shoot some bullets at this.
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 7ff2ea5cd05e..5cea04c05e09 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -524,10 +524,16 @@ static int do_blk_trace_setup(struct request_queue *q,
char *name, dev_t dev,
if (!bt->msg_data)
goto err;
- ret = -ENOENT;
-
- dir = debugfs_lookup(buts->name, blk_debugfs_root);
- if (!dir)
+ /*
+ * When tracing whole make_request drivers (multiqueue) block devices,
+ * reuse the existing debugfs directory created by the block layer on
+ * init. For request-based block devices, all partitions block devices,
+ * and scsi-generic block devices we create a temporary new debugfs
+ * directory that will be removed once the trace ends.
+ */
+ if (queue_is_mq(q))
+ dir = q->debugfs_dir;
+ else
bt->dir = dir = debugfs_create_dir(buts->name,
blk_debugfs_root);
bt->dev = dev;
@@ -565,8 +571,6 @@ static int do_blk_trace_setup(struct request_queue *q, char
*name, dev_t dev,
ret = 0;
err:
- if (dir && !bt->dir)
- dput(dir);
if (ret)
blk_trace_free(bt);
return ret;
