[PATCH] fuse: fix request_end() vs fuse_reset_request() race
The last fix for this function in fact opened up a much more often
triggering race.
It was uncommented tricky code, that was buggy. Add comment, make it less
tricky and fix bug.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 4526da8..f556a0d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -120,9 +120,9 @@
return do_get_request(fc);
}
+/* Must be called with fuse_lock held */
static void fuse_putback_request(struct fuse_conn *fc, struct fuse_req *req)
{
- spin_lock(&fuse_lock);
if (req->preallocated) {
atomic_dec(&fc->num_waiting);
list_add(&req->list, &fc->unused_list);
@@ -134,11 +134,19 @@
fc->outstanding_debt--;
else
up(&fc->outstanding_sem);
- spin_unlock(&fuse_lock);
}
void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
{
+ if (atomic_dec_and_test(&req->count)) {
+ spin_lock(&fuse_lock);
+ fuse_putback_request(fc, req);
+ spin_unlock(&fuse_lock);
+ }
+}
+
+static void fuse_put_request_locked(struct fuse_conn *fc, struct fuse_req *req)
+{
if (atomic_dec_and_test(&req->count))
fuse_putback_request(fc, req);
}
@@ -163,26 +171,36 @@
* still waiting), the 'end' callback is called if given, else the
* reference to the request is released
*
+ * Releasing extra reference for foreground requests must be done
+ * within the same locked region as setting state to finished. This
+ * is because fuse_reset_request() may be called after request is
+ * finished and it must be the sole possessor. If request is
+ * interrupted and put in the background, it will return with an error
+ * and hence never be reset and reused.
+ *
* Called with fuse_lock, unlocks it
*/
static void request_end(struct fuse_conn *fc, struct fuse_req *req)
{
- void (*end) (struct fuse_conn *, struct fuse_req *) = req->end;
- req->end = NULL;
list_del(&req->list);
req->state = FUSE_REQ_FINISHED;
- spin_unlock(&fuse_lock);
- if (req->background) {
+ if (!req->background) {
+ wake_up(&req->waitq);
+ fuse_put_request_locked(fc, req);
+ spin_unlock(&fuse_lock);
+ } else {
+ void (*end) (struct fuse_conn *, struct fuse_req *) = req->end;
+ req->end = NULL;
+ spin_unlock(&fuse_lock);
down_read(&fc->sbput_sem);
if (fc->mounted)
fuse_release_background(req);
up_read(&fc->sbput_sem);
+ if (end)
+ end(fc, req);
+ else
+ fuse_put_request(fc, req);
}
- wake_up(&req->waitq);
- if (end)
- end(fc, req);
- else
- fuse_put_request(fc, req);
}
/*