From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 3/3] aio-use-cancellation-list-lazily-fix Date: Fri, 25 Jan 2013 15:12:51 -0800 Message-ID: <20130125151251.0c90bf4b.akpm@linux-foundation.org> References: <20130124211850.GH26407@google.com> <1359063833-17174-1-git-send-email-koverstreet@google.com> <1359063833-17174-3-git-send-email-koverstreet@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Kent Overstreet , Valdis.Kletnieks@vt.edu, bcrl@kvack.org, zab@zabbo.net, linux-kernel@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org To: Hillf Danton Return-path: In-Reply-To: Sender: owner-linux-aio@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Fri, 25 Jan 2013 21:30:32 +0800 Hillf Danton wrote: > On Fri, Jan 25, 2013 at 5:43 AM, Kent Overstreet wrote: > > The cancellation changes were fubar - we can't cancel a kiocb if it > > doesn't actually have a cancellation callback. > > > > The use of xchg() in aio_complete() was right - there we're marking the > > kiocb as completed - but we need to use cmpxchg() in kiocb_cancel() - a > > lock isn't sufficient since we're synchronizing with aio_complete() > > which isn't taking any locks. > > > > static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb, > > struct io_event *res) > > { > > - kiocb_cancel_fn *cancel; > > + kiocb_cancel_fn *old, *cancel; > > int ret = -EINVAL; > > > > - cancel = xchg(&kiocb->ki_cancel, KIOCB_CANCELLED); > > - if (!cancel || cancel == KIOCB_CANCELLED) > > - return ret; > > + /* > > + * Don't want to set kiocb->ki_cancel = KIOCB_CANCELLED unless it > > + * actually has a cancel function, hence the cmpxchg() > > + */ > > + > > + cancel = ACCESS_ONCE(kiocb->ki_cancel); > > + do { > > + if (!cancel || cancel == KIOCB_CANCELLED) > > + return ret; > > + > > + BUG(); > > Hmm, what is trapped? > > > + old = cancel; > > + cancel = cmpxchg(&kiocb->ki_cancel, old, KIOCB_CANCELLED); > > + } while (cancel != old); erk, I missed that. What earthly sense is there in putting a BUG() in that place. I think I'll delete it and pretend I never saw it :( -- 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