Return-Path: Received: from mail-ig0-f181.google.com ([209.85.213.181]:36024 "EHLO mail-ig0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751823AbbIQOuZ (ORCPT ); Thu, 17 Sep 2015 10:50:25 -0400 Received: by igcrk20 with SMTP id rk20so58320456igc.1 for ; Thu, 17 Sep 2015 07:50:24 -0700 (PDT) Message-ID: <1442501401.12852.1.camel@primarydata.com> Subject: Re: [PATCH] SUNRPC: Fix a race in xs_reset_transport From: Trond Myklebust To: Jeff Layton Cc: "Suzuki K. Poulose" , Anna Schumaker , "J. Bruce Fields" , "David S. Miller" , Linux NFS Mailing List , Linux Kernel Mailing List Date: Thu, 17 Sep 2015 10:50:01 -0400 In-Reply-To: <20150917101847.74ee85ac@synchrony.poochiereds.net> References: <1442332163-9230-1-git-send-email-suzuki.poulose@arm.com> <20150915145229.4e69d5f7@synchrony.poochiereds.net> <20150917101847.74ee85ac@synchrony.poochiereds.net> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, 2015-09-17 at 10:18 -0400, Jeff Layton wrote: > On Thu, 17 Sep 2015 09:38:33 -0400 > Trond Myklebust wrote: > > > On Tue, Sep 15, 2015 at 2:52 PM, Jeff Layton < > > jlayton@poochiereds.net> wrote: > > > On Tue, 15 Sep 2015 16:49:23 +0100 > > > "Suzuki K. Poulose" wrote: > > > > > > > net/sunrpc/xprtsock.c | 9 ++++++++- > > > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c > > > > index 7be90bc..6f4789d 100644 > > > > --- a/net/sunrpc/xprtsock.c > > > > +++ b/net/sunrpc/xprtsock.c > > > > @@ -822,9 +822,16 @@ static void xs_reset_transport(struct > > > > sock_xprt *transport) > > > > if (atomic_read(&transport->xprt.swapper)) > > > > sk_clear_memalloc(sk); > > > > > > > > - kernel_sock_shutdown(sock, SHUT_RDWR); > > > > + if (sock) > > > > + kernel_sock_shutdown(sock, SHUT_RDWR); > > > > > > > > > > Good catch, but...isn't this still racy? What prevents transport > > > ->sock > > > being set to NULL after you assign it to "sock" but before > > > calling > > > kernel_sock_shutdown? > > > > The XPRT_LOCKED state. > > > > IDGI -- if the XPRT_LOCKED bit was supposed to prevent that, then > how could you hit the original race? There should be no concurrent > callers to xs_reset_transport on the same xprt, right? Correct. The only exception is xs_destroy. > AFAICT, that bit is not set in the xprt_destroy codepath, which may > be > the root cause of the problem. How would we take it there anyway? > xprt_destroy is void return, and may not be called in the context of > a > rpc_task. If it's contended, what do we do? Sleep until it's > cleared? > How about the following. 8<-----------------------------------------------------------------