Re: "Cannot allocate memory" on ring creation (not RLIMIT_MEMLOCK)

[Pavel Begunkov <asml.silence@gmail.com>]

On 20/12/2020 13:00, Pavel Begunkov wrote:
> On 20/12/2020 07:13, Josef wrote:
>>> Guys, do you share rings between processes? Explicitly like sending
>>> io_uring fd over a socket, or implicitly e.g. sharing fd tables
>>> (threads), or cloning with copying fd tables (and so taking a ref
>>> to a ring).
>>
>> no in netty we don't share ring between processes
>>
>>> In other words, if you kill all your io_uring applications, does it
>>> go back to normal?
>>
>> no at all, the io-wq worker thread is still running, I literally have
>> to restart the vm to go back to normal(as far as I know is not
>> possible to kill kernel threads right?)
>>
>>> Josef, can you test the patch below instead? Following Jens' idea it
>>> cancels more aggressively when a task is killed or exits. It's based
>>> on [1] but would probably apply fine to for-next.
>>
>> it works, I run several tests with eventfd read op async flag enabled,
>> thanks a lot :) you are awesome guys :)
> 
> Thanks for testing and confirming! Either we forgot something in
> io_ring_ctx_wait_and_kill() and it just can't cancel some requests,
> or we have a dependency that prevents release from happening.
> 
> BTW, apparently that patch causes hangs for unrelated but known
> reasons, so better to not use it, we'll merge something more stable.

I'd really appreciate if you can try one more. I want to know why
the final cleanup doesn't cope  with it.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 941fe9b64fd9..d38fc819648e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8614,6 +8614,10 @@ static int io_remove_personalities(int id, void *p, void *data)
 	return 0;
 }
 
+static void io_cancel_defer_files(struct io_ring_ctx *ctx,
+				  struct task_struct *task,
+				  struct files_struct *files);
+
 static void io_ring_exit_work(struct work_struct *work)
 {
 	struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx,
@@ -8627,6 +8631,8 @@ static void io_ring_exit_work(struct work_struct *work)
 	 */
 	do {
 		io_iopoll_try_reap_events(ctx);
+		io_poll_remove_all(ctx, NULL, NULL);
+		io_kill_timeouts(ctx, NULL, NULL);
 	} while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
 	io_ring_ctx_free(ctx);
 }
@@ -8641,6 +8647,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 		io_cqring_overflow_flush(ctx, true, NULL, NULL);
 	mutex_unlock(&ctx->uring_lock);
 
+	io_cancel_defer_files(ctx, NULL, NULL);
 	io_kill_timeouts(ctx, NULL, NULL);
 	io_poll_remove_all(ctx, NULL, NULL);
 
-- 
Pavel Begunkov