An earlier commit:
b7db41c9e03b ("io_uring: fix regression with always ignoring signals in io_cqring_wait()")
ensured that we didn't get stuck waiting for eventfd reads when it's
registered with the io_uring ring for event notification, but we still
have a gap where the task can be waiting on other events in the kernel
and need a bigger nudge to make forward progress.
Ensure that we use signaled notifications for a task that isn't currently
running, to be certain the work is seen and processed immediately.
Cc: stable@xxxxxxxxxxxxxxx # v5.7+
Reported-by: Josef <josef.grieb@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/io_uring.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index e9b27cdaa735..443eecdfeda9 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1712,21 +1712,27 @@ static int io_req_task_work_add(struct io_kiocb *req, struct callback_head *cb)
struct io_ring_ctx *ctx = req->ctx;
int ret, notify = TWA_RESUME;
+ ret = __task_work_add(tsk, cb);
+ if (unlikely(ret))
+ return ret;
+
/*
* SQPOLL kernel thread doesn't need notification, just a wakeup.
- * If we're not using an eventfd, then TWA_RESUME is always fine,
- * as we won't have dependencies between request completions for
- * other kernel wait conditions.
+ * For any other work, use signaled wakeups if the task isn't
+ * running to avoid dependencies between tasks or threads. If
+ * the issuing task is currently waiting in the kernel on a thread,
+ * and same thread is waiting for a completion event, then we need
+ * to ensure that the issuing task processes task_work. TWA_SIGNAL
+ * is needed for that.
*/
if (ctx->flags & IORING_SETUP_SQPOLL)
notify = 0;
- else if (ctx->cq_ev_fd)
+ else if (READ_ONCE(tsk->state) != TASK_RUNNING)
notify = TWA_SIGNAL;
- ret = task_work_add(tsk, cb, notify);
- if (!ret)
- wake_up_process(tsk);
- return ret;
+ __task_work_notify(tsk, notify);
+ wake_up_process(tsk);
+ return 0;
}
static void __io_req_task_cancel(struct io_kiocb *req, int error)
--
2.28.0
