[PATCH v2] fuse: propagate async RELEASE queue errno in fuse_file_put()

[Li Wang]

fuse_file_put() queues asynchronous FUSE_RELEASE via fuse_simple_background().
When queueing fails, the failure branch always passed -ENOTCONN into
fuse_release_end(). fuse_simple_background() can however fail for multiple
reasons with different return values, such as -ENOMEM or -EINTR. Pass the
actual negative errno into fuse_release_end(). A similar pattern occurs
when fuse_send_readpages() calls fuse_readpages_end(). In that case,
if sending the request fails, fuse_readpages_end() is invoked
directly using the error value returned by the sending function as an argument.
Furthermore, the same applies to fuse_async_req_send() calling
fuse_aio_complete_req(). This patch aligns with those cases.

The parameter "error" is currently unused in fuse_release_end().
While removing it seems like the better choice, however, while fuse_file_put()
calls fuse_release_end() directly if sending the async request fails, it also
registers fuse_release_end() as the success callback. Consequently,
fuse_release_end() must strictly adhere to the callback signature; removing
any parameter would trigger a compilation error. Add an explicit
(void)error in fuse_release_end() so builds that enable
-Wunused-parameter (for example make W=3) stay clean.

Signed-off-by: Li Wang <liwang@xxxxxxxxxx>
---
Changes since v1:
- Amend commit message to clarify the reasoning behind the code changes.

 fs/fuse/file.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 3bdab8d03373..8b7badb7721a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -96,6 +96,8 @@ static void fuse_release_end(struct fuse_args *args, int error)
 {
 	struct fuse_release_args *ra = container_of(args, typeof(*ra), args);
 
+	(void)error;
+
 	iput(ra->inode);
 	kfree(ra);
 }
@@ -117,6 +119,8 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
 			fuse_simple_request(ff->fm, args);
 			fuse_release_end(args, 0);
 		} else {
+			int err;
+
 			/*
 			 * DAX inodes may need to issue a number of synchronous
 			 * request for clearing the mappings.
@@ -124,9 +128,10 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
 			if (ra && ra->inode && FUSE_IS_DAX(ra->inode))
 				args->may_block = true;
 			args->end = fuse_release_end;
-			if (fuse_simple_background(ff->fm, args,
-						   GFP_KERNEL | __GFP_NOFAIL))
-				fuse_release_end(args, -ENOTCONN);
+			err = fuse_simple_background(ff->fm, args,
+						     GFP_KERNEL | __GFP_NOFAIL);
+			if (err)
+				fuse_release_end(args, err);
 		}
 		kfree(ff);
 	}
-- 
2.34.1