From: Uday Shankar ushankar@purestorage.com
Most uring_cmds issued against ublk character devices are serialized because each command affects only one queue, and there is an early check which only allows a single task (the queue's ubq_daemon) to issue uring_cmds against that queue. However, this mechanism does not work for FETCH_REQs, since they are expected before ubq_daemon is set. Since FETCH_REQs are only used at initialization and not in the fast path, serialize them using the per-ublk-device mutex. This fixes a number of data races that were previously possible if a badly behaved ublk server decided to issue multiple FETCH_REQs against the same qid/tag concurrently.
Reported-by: Caleb Sander Mateos csander@purestorage.com Signed-off-by: Uday Shankar ushankar@purestorage.com Signed-off-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20250416035444.99569-2-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk --- drivers/block/ublk_drv.c | 77 +++++++++++++++++++++++++--------------- 1 file changed, 49 insertions(+), 28 deletions(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 4e81505179c6..9345a6d8dbd8 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -1803,8 +1803,8 @@ static void ublk_nosrv_work(struct work_struct *work)
/* device can only be started after all IOs are ready */ static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq) + __must_hold(&ub->mutex) { - mutex_lock(&ub->mutex); ubq->nr_io_ready++; if (ublk_queue_ready(ubq)) { ubq->ubq_daemon = current; @@ -1816,7 +1816,6 @@ static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq) } if (ub->nr_queues_ready == ub->dev_info.nr_hw_queues) complete_all(&ub->completion); - mutex_unlock(&ub->mutex); }
static inline int ublk_check_cmd_op(u32 cmd_op) @@ -1855,6 +1854,52 @@ static inline void ublk_prep_cancel(struct io_uring_cmd *cmd, io_uring_cmd_mark_cancelable(cmd, issue_flags); }
+static int ublk_fetch(struct io_uring_cmd *cmd, struct ublk_queue *ubq, + struct ublk_io *io, __u64 buf_addr) +{ + struct ublk_device *ub = ubq->dev; + int ret = 0; + + /* + * When handling FETCH command for setting up ublk uring queue, + * ub->mutex is the innermost lock, and we won't block for handling + * FETCH, so it is fine even for IO_URING_F_NONBLOCK. + */ + mutex_lock(&ub->mutex); + /* UBLK_IO_FETCH_REQ is only allowed before queue is setup */ + if (ublk_queue_ready(ubq)) { + ret = -EBUSY; + goto out; + } + + /* allow each command to be FETCHed at most once */ + if (io->flags & UBLK_IO_FLAG_ACTIVE) { + ret = -EINVAL; + goto out; + } + + WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV); + + if (ublk_need_map_io(ubq)) { + /* + * FETCH_RQ has to provide IO buffer if NEED GET + * DATA is not enabled + */ + if (!buf_addr && !ublk_need_get_data(ubq)) + goto out; + } else if (buf_addr) { + /* User copy requires addr to be unset */ + ret = -EINVAL; + goto out; + } + + ublk_fill_io_cmd(io, cmd, buf_addr); + ublk_mark_io_ready(ub, ubq); +out: + mutex_unlock(&ub->mutex); + return ret; +} + static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags, const struct ublksrv_io_cmd *ub_cmd) @@ -1907,33 +1952,9 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd, ret = -EINVAL; switch (_IOC_NR(cmd_op)) { case UBLK_IO_FETCH_REQ: - /* UBLK_IO_FETCH_REQ is only allowed before queue is setup */ - if (ublk_queue_ready(ubq)) { - ret = -EBUSY; - goto out; - } - /* - * The io is being handled by server, so COMMIT_RQ is expected - * instead of FETCH_REQ - */ - if (io->flags & UBLK_IO_FLAG_OWNED_BY_SRV) - goto out; - - if (ublk_need_map_io(ubq)) { - /* - * FETCH_RQ has to provide IO buffer if NEED GET - * DATA is not enabled - */ - if (!ub_cmd->addr && !ublk_need_get_data(ubq)) - goto out; - } else if (ub_cmd->addr) { - /* User copy requires addr to be unset */ - ret = -EINVAL; + ret = ublk_fetch(cmd, ubq, io, ub_cmd->addr); + if (ret) goto out; - } - - ublk_fill_io_cmd(io, cmd, ub_cmd->addr); - ublk_mark_io_ready(ub, ubq); break; case UBLK_IO_COMMIT_AND_FETCH_REQ: req = blk_mq_tag_to_rq(ub->tag_set.tags[ub_cmd->q_id], tag);