From 51fecdd2555b3e0e05a78d30093c638d164a32f9 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Tue, 15 Oct 2019 13:46:22 -0400 Subject: [PATCH] virtiofs: Do not end request in submission context Submission context can hold some locks which end request code tries to hold again and deadlock can occur. For example, fc->bg_lock. If a background request is being submitted, it might hold fc->bg_lock and if we could not submit request (because device went away) and tried to end request, then deadlock happens. During testing, I also got a warning from deadlock detection code. So put requests on a list and end requests from a worker thread. I got following warning from deadlock detector. [ 603.137138] WARNING: possible recursive locking detected [ 603.137142] -------------------------------------------- [ 603.137144] blogbench/2036 is trying to acquire lock: [ 603.137149] 00000000f0f51107 (&(&fc->bg_lock)->rlock){+.+.}, at: fuse_request_end+0xdf/0x1c0 [fuse] [ 603.140701] [ 603.140701] but task is already holding lock: [ 603.140703] 00000000f0f51107 (&(&fc->bg_lock)->rlock){+.+.}, at: fuse_simple_background+0x92/0x1d0 [fuse] [ 603.140713] [ 603.140713] other info that might help us debug this: [ 603.140714] Possible unsafe locking scenario: [ 603.140714] [ 603.140715] CPU0 [ 603.140716] ---- [ 603.140716] lock(&(&fc->bg_lock)->rlock); [ 603.140718] lock(&(&fc->bg_lock)->rlock); [ 603.140719] [ 603.140719] *** DEADLOCK *** Signed-off-by: Vivek Goyal Signed-off-by: Miklos Szeredi --- fs/fuse/virtio_fs.c | 37 +++++++++++++++++++++++++++++++++---- 1 file changed, 33 insertions(+), 4 deletions(-) diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c index e22a0c003c3d..7ea58606cc1d 100644 --- a/fs/fuse/virtio_fs.c +++ b/fs/fuse/virtio_fs.c @@ -30,6 +30,7 @@ struct virtio_fs_vq { struct virtqueue *vq; /* protected by ->lock */ struct work_struct done_work; struct list_head queued_reqs; + struct list_head end_reqs; /* End these requests */ struct delayed_work dispatch_work; struct fuse_dev *fud; bool connected; @@ -259,8 +260,27 @@ static void virtio_fs_hiprio_done_work(struct work_struct *work) spin_unlock(&fsvq->lock); } -static void virtio_fs_dummy_dispatch_work(struct work_struct *work) +static void virtio_fs_request_dispatch_work(struct work_struct *work) { + struct fuse_req *req; + struct virtio_fs_vq *fsvq = container_of(work, struct virtio_fs_vq, + dispatch_work.work); + struct fuse_conn *fc = fsvq->fud->fc; + + pr_debug("virtio-fs: worker %s called.\n", __func__); + while (1) { + spin_lock(&fsvq->lock); + req = list_first_entry_or_null(&fsvq->end_reqs, struct fuse_req, + list); + if (!req) { + spin_unlock(&fsvq->lock); + return; + } + + list_del_init(&req->list); + spin_unlock(&fsvq->lock); + fuse_request_end(fc, req); + } } static void virtio_fs_hiprio_dispatch_work(struct work_struct *work) @@ -502,6 +522,7 @@ static int virtio_fs_setup_vqs(struct virtio_device *vdev, names[VQ_HIPRIO] = fs->vqs[VQ_HIPRIO].name; INIT_WORK(&fs->vqs[VQ_HIPRIO].done_work, virtio_fs_hiprio_done_work); INIT_LIST_HEAD(&fs->vqs[VQ_HIPRIO].queued_reqs); + INIT_LIST_HEAD(&fs->vqs[VQ_HIPRIO].end_reqs); INIT_DELAYED_WORK(&fs->vqs[VQ_HIPRIO].dispatch_work, virtio_fs_hiprio_dispatch_work); spin_lock_init(&fs->vqs[VQ_HIPRIO].lock); @@ -511,8 +532,9 @@ static int virtio_fs_setup_vqs(struct virtio_device *vdev, spin_lock_init(&fs->vqs[i].lock); INIT_WORK(&fs->vqs[i].done_work, virtio_fs_requests_done_work); INIT_DELAYED_WORK(&fs->vqs[i].dispatch_work, - virtio_fs_dummy_dispatch_work); + virtio_fs_request_dispatch_work); INIT_LIST_HEAD(&fs->vqs[i].queued_reqs); + INIT_LIST_HEAD(&fs->vqs[i].end_reqs); snprintf(fs->vqs[i].name, sizeof(fs->vqs[i].name), "requests.%u", i - VQ_REQUEST); callbacks[i] = virtio_fs_vq_done; @@ -918,6 +940,7 @@ __releases(fiq->lock) struct fuse_conn *fc; struct fuse_req *req; struct fuse_pqueue *fpq; + struct virtio_fs_vq *fsvq; int ret; WARN_ON(list_empty(&fiq->pending)); @@ -951,7 +974,8 @@ __releases(fiq->lock) smp_mb__after_atomic(); retry: - ret = virtio_fs_enqueue_req(&fs->vqs[queue_id], req); + fsvq = &fs->vqs[queue_id]; + ret = virtio_fs_enqueue_req(fsvq, req); if (ret < 0) { if (ret == -ENOMEM || ret == -ENOSPC) { /* Virtqueue full. Retry submission */ @@ -965,7 +989,12 @@ retry: clear_bit(FR_SENT, &req->flags); list_del_init(&req->list); spin_unlock(&fpq->lock); - fuse_request_end(fc, req); + + /* Can't end request in submission context. Use a worker */ + spin_lock(&fsvq->lock); + list_add_tail(&req->list, &fsvq->end_reqs); + schedule_delayed_work(&fsvq->dispatch_work, 0); + spin_unlock(&fsvq->lock); return; } }