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Message-Id: <20250415-ublk_task_per_io-v4-2-54210b91a46f@purestorage.com>
Date: Tue, 15 Apr 2025 18:59:38 -0600
From: Uday Shankar <ushankar@...estorage.com>
To: Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...nel.dk>,
Caleb Sander Mateos <csander@...estorage.com>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
Uday Shankar <ushankar@...estorage.com>
Subject: [PATCH v4 2/4] ublk: mark ublk_queue as const for
ublk_commit_and_fetch
We now allow multiple tasks to operate on I/Os belonging to the same
queue concurrently. This means that any writes to ublk_queue in the I/O
path are potential sources of data races. Try to prevent these by
marking ublk_queue pointers as const when handling COMMIT_AND_FETCH.
Move the logic for this command into its own function
ublk_commit_and_fetch. Also open code ublk_commit_completion in
ublk_commit_and_fetch to reduce the number of parameters/avoid a
redundant lookup.
Suggested-by: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Uday Shankar <ushankar@...estorage.com>
---
drivers/block/ublk_drv.c | 91 +++++++++++++++++++++++-------------------------
1 file changed, 43 insertions(+), 48 deletions(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 9a0d2547512fc8119460739230599d48d2c2a306..153f67d92248ad45bddd2437b1306bb23df7d1ae 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1518,30 +1518,6 @@ static int ublk_ch_mmap(struct file *filp, struct vm_area_struct *vma)
return remap_pfn_range(vma, vma->vm_start, pfn, sz, vma->vm_page_prot);
}
-static void ublk_commit_completion(struct ublk_device *ub,
- const struct ublksrv_io_cmd *ub_cmd)
-{
- u32 qid = ub_cmd->q_id, tag = ub_cmd->tag;
- struct ublk_queue *ubq = ublk_get_queue(ub, qid);
- struct ublk_io *io = &ubq->ios[tag];
- struct request *req;
-
- /* now this cmd slot is owned by nbd driver */
- io->flags &= ~UBLK_IO_FLAG_OWNED_BY_SRV;
- io->res = ub_cmd->result;
-
- /* find the io request and complete */
- req = blk_mq_tag_to_rq(ub->tag_set.tags[qid], tag);
- if (WARN_ON_ONCE(unlikely(!req)))
- return;
-
- if (req_op(req) == REQ_OP_ZONE_APPEND)
- req->__sector = ub_cmd->zone_append_lba;
-
- if (likely(!blk_should_fake_timeout(req->q)))
- ublk_put_req_ref(ubq, req);
-}
-
/*
* Called from io task context via cancel fn, meantime quiesce ublk
* blk-mq queue, so we are called exclusively with blk-mq and io task
@@ -1918,6 +1894,45 @@ static int ublk_unregister_io_buf(struct io_uring_cmd *cmd,
return io_buffer_unregister_bvec(cmd, index, issue_flags);
}
+static int ublk_commit_and_fetch(const struct ublk_queue *ubq,
+ struct ublk_io *io, struct io_uring_cmd *cmd,
+ const struct ublksrv_io_cmd *ub_cmd,
+ struct request *req)
+{
+ if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
+ return -EINVAL;
+
+ if (ublk_need_map_io(ubq)) {
+ /*
+ * COMMIT_AND_FETCH_REQ has to provide IO buffer if
+ * NEED GET DATA is not enabled or it is Read IO.
+ */
+ if (!ub_cmd->addr && (!ublk_need_get_data(ubq) ||
+ req_op(req) == REQ_OP_READ))
+ return -EINVAL;
+ } else if (req_op(req) != REQ_OP_ZONE_APPEND && ub_cmd->addr) {
+ /*
+ * User copy requires addr to be unset when command is
+ * not zone append
+ */
+ return -EINVAL;
+ }
+
+ ublk_fill_io_cmd(io, cmd, ub_cmd->addr);
+
+ /* now this cmd slot is owned by ublk driver */
+ io->flags &= ~UBLK_IO_FLAG_OWNED_BY_SRV;
+ io->res = ub_cmd->result;
+
+ if (req_op(req) == REQ_OP_ZONE_APPEND)
+ req->__sector = ub_cmd->zone_append_lba;
+
+ if (likely(!blk_should_fake_timeout(req->q)))
+ ublk_put_req_ref(ubq, req);
+
+ return -EIOCBQUEUED;
+}
+
static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
unsigned int issue_flags,
const struct ublksrv_io_cmd *ub_cmd)
@@ -1928,7 +1943,6 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
u32 cmd_op = cmd->cmd_op;
unsigned tag = ub_cmd->tag;
int ret = -EINVAL;
- struct request *req;
pr_devel("%s: received: cmd op %d queue %d tag %d result %d\n",
__func__, cmd->cmd_op, ub_cmd->q_id, tag,
@@ -2004,30 +2018,11 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
io->task = get_task_struct(current);
break;
case UBLK_IO_COMMIT_AND_FETCH_REQ:
- req = blk_mq_tag_to_rq(ub->tag_set.tags[ub_cmd->q_id], tag);
-
- if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
+ ret = ublk_commit_and_fetch(
+ ubq, io, cmd, ub_cmd,
+ blk_mq_tag_to_rq(ub->tag_set.tags[ub_cmd->q_id], tag));
+ if (ret != -EIOCBQUEUED)
goto out;
-
- if (ublk_need_map_io(ubq)) {
- /*
- * COMMIT_AND_FETCH_REQ has to provide IO buffer if
- * NEED GET DATA is not enabled or it is Read IO.
- */
- if (!ub_cmd->addr && (!ublk_need_get_data(ubq) ||
- req_op(req) == REQ_OP_READ))
- goto out;
- } else if (req_op(req) != REQ_OP_ZONE_APPEND && ub_cmd->addr) {
- /*
- * User copy requires addr to be unset when command is
- * not zone append
- */
- ret = -EINVAL;
- goto out;
- }
-
- ublk_fill_io_cmd(io, cmd, ub_cmd->addr);
- ublk_commit_completion(ub, ub_cmd);
break;
case UBLK_IO_NEED_GET_DATA:
if (!(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV))
--
2.34.1
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