Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758981AbZCOUJ0 (ORCPT ); Sun, 15 Mar 2009 16:09:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758167AbZCOUJL (ORCPT ); Sun, 15 Mar 2009 16:09:11 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:47890 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753292AbZCOUJK (ORCPT ); Sun, 15 Mar 2009 16:09:10 -0400 X-AuthUser: davidel@xmailserver.org Date: Sun, 15 Mar 2009 13:08:44 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@makko.or.mcafeemobile.com To: Linux Kernel Mailing List cc: Benjamin LaHaise , Trond Myklebust , Andrew Morton , Eric Dumazet , linux-aio , zach.brown@oracle.com Subject: [patch] eventfd - remove fput() call from possible IRQ context (2nd rev) In-Reply-To: <20090315174445.GD18305@kvack.org> Message-ID: References: <49B89B22.7080303@cosmosbay.com> <20090311224712.fb8db075.akpm@linux-foundation.org> <49B8A75E.6040409@cosmosbay.com> <20090311233903.f036027a.akpm@linux-foundation.org> <1236986902.7265.73.camel@heimdal.trondhjem.org> <1237003328.7265.98.camel@heimdal.trondhjem.org> <20090315174445.GD18305@kvack.org> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4419 Lines: 133 The following patch remove a possible source of fput() call from inside IRQ context. Myself, like Eric, wasn't able to reproduce an fput() call from IRQ context, but conceptually the bug is there. This patch adds an optimization similar to the one we already do on ->ki_filp, on ->ki_eventfd. Playing with ->f_count directly is not pretty in general, but the alternative here would be to add a brand new delayed fput() infrastructure, that I'm not sure is worth it. On Sun, 15 Mar 2009, Benjamin LaHaise wrote: > This looks reasonably sane, the only concern I have with it is that I think > it logically makes more sense to use the same convention for fi_filp and > ki_eventfd, as the different in IS_ERR vs checking for NULL is a bit > confusing. Aside from that, it looks like it should fix the problem > correctly. Makes sense. Signed-off-by: Davide Libenzi - Davide --- fs/aio.c | 37 +++++++++++++++++++++++++++---------- 1 file changed, 27 insertions(+), 10 deletions(-) Index: linux-2.6.mod/fs/aio.c =================================================================== --- linux-2.6.mod.orig/fs/aio.c 2009-03-14 09:24:12.000000000 -0700 +++ linux-2.6.mod/fs/aio.c 2009-03-15 12:54:10.000000000 -0700 @@ -443,7 +443,7 @@ static struct kiocb *__aio_get_req(struc req->private = NULL; req->ki_iovec = NULL; INIT_LIST_HEAD(&req->ki_run_list); - req->ki_eventfd = ERR_PTR(-EINVAL); + req->ki_eventfd = NULL; /* Check if the completion queue has enough free space to * accept an event from this io. @@ -485,8 +485,6 @@ static inline void really_put_req(struct { assert_spin_locked(&ctx->ctx_lock); - if (!IS_ERR(req->ki_eventfd)) - fput(req->ki_eventfd); if (req->ki_dtor) req->ki_dtor(req); if (req->ki_iovec != &req->ki_inline_vec) @@ -508,8 +506,11 @@ static void aio_fput_routine(struct work list_del(&req->ki_list); spin_unlock_irq(&fput_lock); - /* Complete the fput */ - __fput(req->ki_filp); + /* Complete the fput(s) */ + if (req->ki_filp != NULL) + __fput(req->ki_filp); + if (req->ki_eventfd != NULL) + __fput(req->ki_eventfd); /* Link the iocb into the context's free list */ spin_lock_irq(&ctx->ctx_lock); @@ -527,12 +528,14 @@ static void aio_fput_routine(struct work */ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req) { + int schedule_putreq = 0; + dprintk(KERN_DEBUG "aio_put(%p): f_count=%ld\n", req, atomic_long_read(&req->ki_filp->f_count)); assert_spin_locked(&ctx->ctx_lock); - req->ki_users --; + req->ki_users--; BUG_ON(req->ki_users < 0); if (likely(req->ki_users)) return 0; @@ -540,10 +543,23 @@ static int __aio_put_req(struct kioctx * req->ki_cancel = NULL; req->ki_retry = NULL; - /* Must be done under the lock to serialise against cancellation. - * Call this aio_fput as it duplicates fput via the fput_work. + /* + * Try to optimize the aio and eventfd file* puts, by avoiding to + * schedule work in case it is not __fput() time. In normal cases, + * we wouldn not be holding the last reference to the file*, so + * this function will be executed w/out any aio kthread wakeup. */ - if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) { + if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) + schedule_putreq++; + else + req->ki_filp = NULL; + if (unlikely(req->ki_eventfd != NULL)) { + if (unlikely(atomic_long_dec_and_test(&req->ki_eventfd->f_count))) + schedule_putreq++; + else + req->ki_eventfd = NULL; + } + if (unlikely(schedule_putreq)) { get_ioctx(ctx); spin_lock(&fput_lock); list_add(&req->ki_list, &fput_head); @@ -1009,7 +1025,7 @@ int aio_complete(struct kiocb *iocb, lon * eventfd. The eventfd_signal() function is safe to be called * from IRQ context. */ - if (!IS_ERR(iocb->ki_eventfd)) + if (iocb->ki_eventfd != NULL) eventfd_signal(iocb->ki_eventfd, 1); put_rq: @@ -1608,6 +1624,7 @@ static int io_submit_one(struct kioctx * req->ki_eventfd = eventfd_fget((int) iocb->aio_resfd); if (IS_ERR(req->ki_eventfd)) { ret = PTR_ERR(req->ki_eventfd); + req->ki_eventfd = NULL; goto out_put_req; } } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/