fuse: mark DAX inode releases as blocking

Commit 26e5c67deb2e ("fuse: fix livelock in synchronous file put from
fuseblk workers") made fputs on closing files always asynchronous.

As cleaning up DAX inodes may require issuing a number of synchronous
request for releasing the mappings, completing the release request from
the worker thread may lead to it hanging like this:

[   21.386751] Workqueue: events virtio_fs_requests_done_work
[   21.386769] Call trace:
[   21.386770]  __switch_to+0xe4/0x140
[   21.386780]  __schedule+0x294/0x72c
[   21.386787]  schedule+0x24/0x90
[   21.386794]  request_wait_answer+0x184/0x298
[   21.386799]  __fuse_simple_request+0x1f4/0x320
[   21.386805]  fuse_send_removemapping+0x80/0xa0
[   21.386810]  dmap_removemapping_list+0xac/0xfc
[   21.386814]  inode_reclaim_dmap_range.constprop.0+0xd0/0x204
[   21.386820]  fuse_dax_inode_cleanup+0x28/0x5c
[   21.386825]  fuse_evict_inode+0x120/0x190
[   21.386834]  evict+0x188/0x320
[   21.386847]  iput_final+0xb0/0x20c
[   21.386854]  iput+0xa0/0xbc
[   21.386862]  fuse_release_end+0x18/0x2c
[   21.386868]  fuse_request_end+0x9c/0x2c0
[   21.386872]  virtio_fs_request_complete+0x150/0x384
[   21.386879]  virtio_fs_requests_done_work+0x18c/0x37c
[   21.386885]  process_one_work+0x15c/0x2e8
[   21.386891]  worker_thread+0x278/0x480
[   21.386898]  kthread+0xd0/0xdc
[   21.386902]  ret_from_fork+0x10/0x20

Here, the virtio-fs worker_thread is waiting on request_wait_answer()
for a reply from the virtio-fs server that is already in the virtqueue
but will never be processed since it's that same worker thread the one
in charge of consuming the elements from the virtqueue.

To address this issue, when relesing a DAX inode mark the operation as
potentially blocking. Doing this will ensure these release requests are
processed on a different worker thread.

Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b1bb7153cb785f604307f34308e8d161e7596585..30a74f61caf00b1a040e17e8676b0350c4876866 100644 (file)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -117,6 +117,12 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
                        fuse_simple_request(ff->fm, args);
                        fuse_release_end(ff->fm, args, 0);
                } else {
+                       /*
+                        * DAX inodes may need to issue a number of synchronous
+                        * request for clearing the mappings.
+                        */
+                       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))