[PATCH v2] fuse: permit freezing while waiting for request answer

[Sergey Senozhatsky]

Suspend freezes tasks in random order and doesn't take into
consideration producer-consumer dependency that may exist
between tasks.  One example where this can cause issues is:
fuse server getting frozen ahead of clients, which then get
stuck waiting for req answers that never come (the server
is already frozen).

Make all wait-event calls in request_wait_answer() freezer-friendly.

This, however, doesn't address all cases.  E.g. in-place
PM-freeze of a request_wait_answer() task holding a contended
VFS lock still will block suspend.

Note: this uses TASK_FREEZABLE, not TASK_FREEZABLE_UNSAFE,
which may trigger debug_locks warning during suspend (if
request_wait_answer() task holds some locks at the time
of freeze.)

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---

 fs/fuse/dev.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 34106f6e66a0..42098ddc2587 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -701,8 +701,9 @@ static void request_wait_answer(struct fuse_req *req)
 
 	if (!fch->no_interrupt) {
 		/* Any signal may interrupt this */
-		err = wait_event_interruptible(req->waitq,
-					test_bit(FR_FINISHED, &req->flags));
+		err = wait_event_state(req->waitq,
+				       test_bit(FR_FINISHED, &req->flags),
+				       (TASK_INTERRUPTIBLE | TASK_FREEZABLE));
 		if (!err)
 			return;
 
@@ -717,8 +718,9 @@ static void request_wait_answer(struct fuse_req *req)
 		bool removed;
 
 		/* Only fatal signals may interrupt this */
-		err = wait_event_killable(req->waitq,
-					test_bit(FR_FINISHED, &req->flags));
+		err = wait_event_state(req->waitq,
+				       test_bit(FR_FINISHED, &req->flags),
+				       (TASK_KILLABLE | TASK_FREEZABLE));
 		if (!err)
 			return;
 
@@ -740,7 +742,8 @@ static void request_wait_answer(struct fuse_req *req)
 	 * Either request is already in userspace, or it was forced.
 	 * Wait it out.
 	 */
-	wait_event(req->waitq, test_bit(FR_FINISHED, &req->flags));
+	wait_event_state(req->waitq, test_bit(FR_FINISHED, &req->flags),
+			 (TASK_UNINTERRUPTIBLE | TASK_FREEZABLE));
 }
 
 static void __fuse_request_send(struct fuse_req *req)
-- 
2.55.0.737.g08866a6d13-goog