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ublk: properly serialize all FETCH_REQs

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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>
This commit is contained in:
Uday Shankar 2025-04-16 11:54:35 +08:00 committed by Jens Axboe
parent 3bf540609c
commit b69b8edfb2
1 changed files with 49 additions and 28 deletions
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77
drivers/block/ublk_drv.c
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@ -1832,8 +1832,8 @@ 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;
@ -1845,7 +1845,6 @@ 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 void ublk_handle_need_get_data(struct ublk_device *ub, int q_id,
@ -1929,6 +1928,52 @@ static int ublk_unregister_io_buf(struct io_uring_cmd *cmd,
return io_buffer_unregister_bvec(cmd, index, 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)
@ -1985,33 +2030,9 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
case UBLK_IO_UNREGISTER_IO_BUF:
return ublk_unregister_io_buf(cmd, ub_cmd->addr, issue_flags);
case UBLK_IO_FETCH_REQ:
/* UBLK_IO_FETCH_REQ is only allowed before queue is setup */
if (ublk_queue_ready(ubq)) {
ret = -EBUSY;
ret = ublk_fetch(cmd, ubq, io, ub_cmd->addr);
if (ret)
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;
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);