From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jann Horn Subject: Re: [PATCH 05/18] Add io_uring IO interface Date: Tue, 29 Jan 2019 02:32:49 +0100 Message-ID: References: <20190128213538.13486-1-axboe@kernel.dk> <20190128213538.13486-6-axboe@kernel.dk> <9170f97f-bea3-04b9-71db-a0f250d1f610@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <9170f97f-bea3-04b9-71db-a0f250d1f610@kernel.dk> Sender: owner-linux-aio@kvack.org To: Jens Axboe Cc: linux-aio@kvack.org, linux-block@vger.kernel.org, linux-man , Linux API , hch@lst.de, jmoyer@redhat.com, Avi Kivity List-Id: linux-man@vger.kernel.org On Tue, Jan 29, 2019 at 2:31 AM Jens Axboe wrote: > On 1/28/19 6:29 PM, Jann Horn wrote: > > On Mon, Jan 28, 2019 at 10:35 PM Jens Axboe wrote: > >> The submission queue (SQ) and completion queue (CQ) rings are shared > >> between the application and the kernel. This eliminates the need to > >> copy data back and forth to submit and complete IO. > > [...] > >> +static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx) > >> +{ > >> + struct io_kiocb *req; > >> + > >> + /* safe to use the non tryget, as we're inside ring ref already */ > >> + percpu_ref_get(&ctx->refs); > > > > Is that true? In the path io_sq_thread() -> io_submit_sqes() -> > > io_submit_sqe() -> io_get_req(), I don't see anything that's already > > holding a reference for you. Is the worker thread holding a reference > > somewhere that I'm missing? > > If the thread is alive, then the ctx is alive. Before we drop the last > ref to the ctx (and kill it), we wait for the thread to exit. Where in __io_uring_register() are you waiting for the thread to exit before killing it? As far as I can tell, you come straight in from syscall context, take a mutex, and do percpu_ref_kill(). -- To unsubscribe, send a message with 'unsubscribe linux-aio' in the body to majordomo@kvack.org. For more info on Linux AIO, see: http://www.kvack.org/aio/ Don't email: aart@kvack.org