From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [PATCH 10/32] aio: implement IOCB_CMD_POLL Date: Sun, 20 May 2018 08:33:39 +0100 Message-ID: <20180520073332.GA30522@ZenIV.linux.org.uk> References: <20180515194833.6906-1-hch@lst.de> <20180515194833.6906-11-hch@lst.de> <20180520053219.GZ30522@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180520053219.GZ30522@ZenIV.linux.org.uk> Sender: owner-linux-aio@kvack.org To: Christoph Hellwig Cc: Avi Kivity , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-api@vger.kernel.org On Sun, May 20, 2018 at 06:32:25AM +0100, Al Viro wrote: > > + spin_lock_irqsave(&ctx->ctx_lock, flags); > > + list_add_tail(&aiocb->ki_list, &ctx->delayed_cancel_reqs); > > + spin_unlock(&ctx->ctx_lock); > > ... and io_cancel(2) comes, finds it and inhume^Wcompletes it, leaving us to... > > > + spin_lock(&req->head->lock); > > ... get buggered on attempt to dereference a pointer fetched from freed and > reused object. FWIW, how painful would it be to pull the following trick: * insert into wait queue under ->ctx_lock * have wakeup do schedule_work() with aio_complete() done from that * have ->ki_cancel() grab queue lock, remove from queue and use the same schedule_work() That way you'd get ->ki_cancel() with the same semantics as originally for everything - "ask politely to finish ASAP", and called in the same locking environment for everyone - under ->ctx_lock, that is. queue lock nests inside ->ctx_lock; no magical flags, etc. The cost is schedule_work() for each async poll-related completion as you have for fsync. I don't know whether that's too costly or not; it certainly simplifies the things, but whether it's OK performance-wise... Comments? -- 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