On Thu, Nov 7, 2024 at 9:04 AM Bernd Schubert <bschubert@xxxxxxx> wrote:
>
> When the fuse-server terminates while the fuse-client or kernel
> still has queued URING_CMDs, these commands retain references
> to the struct file used by the fuse connection. This prevents
> fuse_dev_release() from being invoked, resulting in a hung mount
> point.
Could you explain the flow of what happens after a fuse server
terminates? How does that trigger the IO_URING_F_CANCEL uring cmd?
>
> This patch addresses the issue by making queued URING_CMDs
> cancelable, allowing fuse_dev_release() to proceed as expected
> and preventing the mount point from hanging.
>
> Signed-off-by: Bernd Schubert <bschubert@xxxxxxx>
> ---
> fs/fuse/dev_uring.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 70 insertions(+), 6 deletions(-)
>
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index 6af515458695ccb2e32cc8c62c45471e6710c15f..b465da41c42c47eaf69f09bab1423061bc8fcc68 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -23,6 +23,7 @@ MODULE_PARM_DESC(enable_uring,
>
> struct fuse_uring_cmd_pdu {
> struct fuse_ring_ent *ring_ent;
> + struct fuse_ring_queue *queue;
> };
>
> /*
> @@ -382,6 +383,61 @@ void fuse_uring_stop_queues(struct fuse_ring *ring)
> }
> }
>
> +/*
> + * Handle IO_URING_F_CANCEL, typically should come on daemon termination
> + */
> +static void fuse_uring_cancel(struct io_uring_cmd *cmd,
> + unsigned int issue_flags, struct fuse_conn *fc)
> +{
> + struct fuse_uring_cmd_pdu *pdu = (struct fuse_uring_cmd_pdu *)cmd->pdu;
> + struct fuse_ring_queue *queue = pdu->queue;
> + struct fuse_ring_ent *ent;
> + bool found = false;
> + bool need_cmd_done = false;
> +
> + spin_lock(&queue->lock);
> +
> + /* XXX: This is cumbersome for large queues. */
> + list_for_each_entry(ent, &queue->ent_avail_queue, list) {
> + if (pdu->ring_ent == ent) {
> + found = true;
> + break;
> + }
> + }
> +
> + if (!found) {
> + pr_info("qid=%d Did not find ent=%p", queue->qid, ent);
> + spin_unlock(&queue->lock);
> + return;
> + }
> +
> + if (ent->state == FRRS_WAIT) {
> + ent->state = FRRS_USERSPACE;
> + list_move(&ent->list, &queue->ent_in_userspace);
> + need_cmd_done = true;
> + }
> + spin_unlock(&queue->lock);
> +
> + if (need_cmd_done)
> + io_uring_cmd_done(cmd, -ENOTCONN, 0, issue_flags);
> +
> + /*
> + * releasing the last entry should trigger fuse_dev_release() if
> + * the daemon was terminated
> + */
> +}
> +
> +static void fuse_uring_prepare_cancel(struct io_uring_cmd *cmd, int issue_flags,
> + struct fuse_ring_ent *ring_ent)
> +{
> + struct fuse_uring_cmd_pdu *pdu = (struct fuse_uring_cmd_pdu *)cmd->pdu;
> +
> + pdu->ring_ent = ring_ent;
> + pdu->queue = ring_ent->queue;
> +
> + io_uring_cmd_mark_cancelable(cmd, issue_flags);
> +}
> +
> /*
> * Checks for errors and stores it into the request
> */
> @@ -606,7 +662,8 @@ static int fuse_uring_send_next_to_ring(struct fuse_ring_ent *ring_ent)
> * Put a ring request onto hold, it is no longer used for now.
> */
> static void fuse_uring_ent_avail(struct fuse_ring_ent *ring_ent,
> - struct fuse_ring_queue *queue)
> + struct fuse_ring_queue *queue,
> + unsigned int issue_flags)
> __must_hold(&queue->lock)
> {
> struct fuse_ring *ring = queue->ring;
> @@ -626,6 +683,7 @@ static void fuse_uring_ent_avail(struct fuse_ring_ent *ring_ent,
> list_move(&ring_ent->list, &queue->ent_avail_queue);
>
> ring_ent->state = FRRS_WAIT;
> + fuse_uring_prepare_cancel(ring_ent->cmd, issue_flags, ring_ent);
> }
>
> /* Used to find the request on SQE commit */
> @@ -729,7 +787,8 @@ static void fuse_uring_commit(struct fuse_ring_ent *ring_ent,
> * Get the next fuse req and send it
> */
> static void fuse_uring_next_fuse_req(struct fuse_ring_ent *ring_ent,
> - struct fuse_ring_queue *queue)
> + struct fuse_ring_queue *queue,
> + unsigned int issue_flags)
> {
> int has_next, err;
> int prev_state = ring_ent->state;
> @@ -738,7 +797,7 @@ static void fuse_uring_next_fuse_req(struct fuse_ring_ent *ring_ent,
> spin_lock(&queue->lock);
> has_next = fuse_uring_ent_assign_req(ring_ent);
> if (!has_next) {
> - fuse_uring_ent_avail(ring_ent, queue);
> + fuse_uring_ent_avail(ring_ent, queue, issue_flags);
> spin_unlock(&queue->lock);
> break; /* no request left */
> }
> @@ -813,7 +872,7 @@ static int fuse_uring_commit_fetch(struct io_uring_cmd *cmd, int issue_flags,
> * and fetching is done in one step vs legacy fuse, which has separated
> * read (fetch request) and write (commit result).
> */
> - fuse_uring_next_fuse_req(ring_ent, queue);
> + fuse_uring_next_fuse_req(ring_ent, queue, issue_flags);
> return 0;
> }
>
> @@ -853,7 +912,7 @@ static void _fuse_uring_fetch(struct fuse_ring_ent *ring_ent,
> struct fuse_ring *ring = queue->ring;
>
> spin_lock(&queue->lock);
> - fuse_uring_ent_avail(ring_ent, queue);
> + fuse_uring_ent_avail(ring_ent, queue, issue_flags);
> ring_ent->cmd = cmd;
> spin_unlock(&queue->lock);
>
> @@ -1021,6 +1080,11 @@ int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
> if (fc->aborted)
> goto out;
>
> + if ((unlikely(issue_flags & IO_URING_F_CANCEL))) {
> + fuse_uring_cancel(cmd, issue_flags, fc);
> + return 0;
> + }
> +
> switch (cmd_op) {
> case FUSE_URING_REQ_FETCH:
> err = fuse_uring_fetch(cmd, issue_flags, fc);
> @@ -1080,7 +1144,7 @@ fuse_uring_send_req_in_task(struct io_uring_cmd *cmd,
>
> return;
> err:
> - fuse_uring_next_fuse_req(ring_ent, queue);
> + fuse_uring_next_fuse_req(ring_ent, queue, issue_flags);
> }
>
> /* queue a fuse request and send it if a ring entry is available */
>
> --
> 2.43.0
>
