In well-done ublk server implementation, ublk io command won't be
linked into any link chain. Meantime they are always handled in no-wait
style, so basically io cmd is always handled in submitter task context.
However, the server may set IOSQE_ASYNC, or io command is linked to one
chain mistakenly, then we may still run into io-wq context and
ctx->uring_lock isn't held.
So in case of IO_URING_F_UNLOCKED, schedule this command by
io_uring_cmd_complete_in_task to force running it in submitter task. Then
ublk_ch_uring_cmd_local() is guaranteed to run with context uring_lock held,
and we needn't to worry about sync among submission code path any more.
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
drivers/block/ublk_drv.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 9b3c0b3dd36e..46d499d96ca3 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1810,7 +1810,8 @@ static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
return NULL;
}
-static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
+static inline int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd,
+ unsigned int issue_flags)
{
/*
* Not necessary for async retry, but let's keep it simple and always
@@ -1824,9 +1825,28 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
.addr = READ_ONCE(ub_src->addr)
};
+ WARN_ON_ONCE(issue_flags & IO_URING_F_UNLOCKED);
+
return __ublk_ch_uring_cmd(cmd, issue_flags, &ub_cmd);
}
+static void ublk_ch_uring_cmd_cb(struct io_uring_cmd *cmd,
+ unsigned int issue_flags)
+{
+ ublk_ch_uring_cmd_local(cmd, issue_flags);
+}
+
+static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
+{
+ /* well-implemented server won't run into unlocked */
+ if (unlikely(issue_flags & IO_URING_F_UNLOCKED)) {
+ io_uring_cmd_complete_in_task(cmd, ublk_ch_uring_cmd_cb);
+ return -EIOCBQUEUED;
+ }
+
+ return ublk_ch_uring_cmd_local(cmd, issue_flags);
+}
+
static inline bool ublk_check_ubuf_dir(const struct request *req,
int ubuf_dir)
{
--
2.41.0
