From: Vivek Goyal vgoyal@redhat.com
[ Upstream commit bb737bbe48bea9854455cb61ea1dc06e92ce586c ]
In virtiofs (unlike in regular fuse) processing of async replies is serialized. This can result in a deadlock in rare corner cases when there's a circular dependency between the completion of two or more async replies.
Such a deadlock can be reproduced with xfstests:generic/503 if TEST_DIR == SCRATCH_MNT (which is a misconfiguration):
- Process A is waiting for page lock in worker thread context and blocked (virtio_fs_requests_done_work()). - Process B is holding page lock and waiting for pending writes to finish (fuse_wait_on_page_writeback()). - Write requests are waiting in virtqueue and can't complete because worker thread is blocked on page lock (process A).
Fix this by creating a unique work_struct for each async reply that can block (O_DIRECT read).
Fixes: a62a8ef9d97d ("virtio-fs: add virtiofs filesystem") Signed-off-by: Vivek Goyal vgoyal@redhat.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/fuse/file.c | 1 + fs/fuse/fuse_i.h | 1 + fs/fuse/virtio_fs.c | 106 +++++++++++++++++++++++++++++--------------- 3 files changed, 73 insertions(+), 35 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 3dd37a998ea9..713d55a61890 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -712,6 +712,7 @@ static ssize_t fuse_async_req_send(struct fuse_conn *fc, spin_unlock(&io->lock);
ia->ap.args.end = fuse_aio_complete_req; + ia->ap.args.may_block = io->should_dirty; err = fuse_simple_background(fc, &ia->ap.args, GFP_KERNEL); if (err) fuse_aio_complete_req(fc, &ia->ap.args, err); diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index ca344bf71404..d7cde216fc87 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -249,6 +249,7 @@ struct fuse_args { bool out_argvar:1; bool page_zeroing:1; bool page_replace:1; + bool may_block:1; struct fuse_in_arg in_args[3]; struct fuse_arg out_args[2]; void (*end)(struct fuse_conn *fc, struct fuse_args *args, int error); diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c index a5c86048b96e..7505f8102762 100644 --- a/fs/fuse/virtio_fs.c +++ b/fs/fuse/virtio_fs.c @@ -55,6 +55,12 @@ struct virtio_fs_forget { struct list_head list; };
+struct virtio_fs_req_work { + struct fuse_req *req; + struct virtio_fs_vq *fsvq; + struct work_struct done_work; +}; + static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq, struct fuse_req *req, bool in_flight);
@@ -443,19 +449,67 @@ static void copy_args_from_argbuf(struct fuse_args *args, struct fuse_req *req) }
/* Work function for request completion */ +static void virtio_fs_request_complete(struct fuse_req *req, + struct virtio_fs_vq *fsvq) +{ + struct fuse_pqueue *fpq = &fsvq->fud->pq; + struct fuse_conn *fc = fsvq->fud->fc; + struct fuse_args *args; + struct fuse_args_pages *ap; + unsigned int len, i, thislen; + struct page *page; + + /* + * TODO verify that server properly follows FUSE protocol + * (oh.uniq, oh.len) + */ + args = req->args; + copy_args_from_argbuf(args, req); + + if (args->out_pages && args->page_zeroing) { + len = args->out_args[args->out_numargs - 1].size; + ap = container_of(args, typeof(*ap), args); + for (i = 0; i < ap->num_pages; i++) { + thislen = ap->descs[i].length; + if (len < thislen) { + WARN_ON(ap->descs[i].offset); + page = ap->pages[i]; + zero_user_segment(page, len, thislen); + len = 0; + } else { + len -= thislen; + } + } + } + + spin_lock(&fpq->lock); + clear_bit(FR_SENT, &req->flags); + spin_unlock(&fpq->lock); + + fuse_request_end(fc, req); + spin_lock(&fsvq->lock); + dec_in_flight_req(fsvq); + spin_unlock(&fsvq->lock); +} + +static void virtio_fs_complete_req_work(struct work_struct *work) +{ + struct virtio_fs_req_work *w = + container_of(work, typeof(*w), done_work); + + virtio_fs_request_complete(w->req, w->fsvq); + kfree(w); +} + static void virtio_fs_requests_done_work(struct work_struct *work) { struct virtio_fs_vq *fsvq = container_of(work, struct virtio_fs_vq, done_work); struct fuse_pqueue *fpq = &fsvq->fud->pq; - struct fuse_conn *fc = fsvq->fud->fc; struct virtqueue *vq = fsvq->vq; struct fuse_req *req; - struct fuse_args_pages *ap; struct fuse_req *next; - struct fuse_args *args; - unsigned int len, i, thislen; - struct page *page; + unsigned int len; LIST_HEAD(reqs);
/* Collect completed requests off the virtqueue */ @@ -473,38 +527,20 @@ static void virtio_fs_requests_done_work(struct work_struct *work)
/* End requests */ list_for_each_entry_safe(req, next, &reqs, list) { - /* - * TODO verify that server properly follows FUSE protocol - * (oh.uniq, oh.len) - */ - args = req->args; - copy_args_from_argbuf(args, req); - - if (args->out_pages && args->page_zeroing) { - len = args->out_args[args->out_numargs - 1].size; - ap = container_of(args, typeof(*ap), args); - for (i = 0; i < ap->num_pages; i++) { - thislen = ap->descs[i].length; - if (len < thislen) { - WARN_ON(ap->descs[i].offset); - page = ap->pages[i]; - zero_user_segment(page, len, thislen); - len = 0; - } else { - len -= thislen; - } - } - } - - spin_lock(&fpq->lock); - clear_bit(FR_SENT, &req->flags); list_del_init(&req->list); - spin_unlock(&fpq->lock);
- fuse_request_end(fc, req); - spin_lock(&fsvq->lock); - dec_in_flight_req(fsvq); - spin_unlock(&fsvq->lock); + /* blocking async request completes in a worker context */ + if (req->args->may_block) { + struct virtio_fs_req_work *w; + + w = kzalloc(sizeof(*w), GFP_NOFS | __GFP_NOFAIL); + INIT_WORK(&w->done_work, virtio_fs_complete_req_work); + w->fsvq = fsvq; + w->req = req; + schedule_work(&w->done_work); + } else { + virtio_fs_request_complete(req, fsvq); + } } }