Return-Path: Received: from userp1040.oracle.com ([156.151.31.81]:40759 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbbGVVQD convert rfc822-to-8bit (ORCPT ); Wed, 22 Jul 2015 17:16:03 -0400 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Subject: Re: [PATCH] SUNRPC: Fix a backchannel deadlock From: Chuck Lever In-Reply-To: Date: Wed, 22 Jul 2015 17:15:58 -0400 Cc: Linux NFS Mailing List Message-Id: References: <1437597373-19455-1-git-send-email-trond.myklebust@primarydata.com> <0E5E2AA6-6FCF-4A0E-94E3-91A2D529B58B@oracle.com> To: Trond Myklebust Sender: linux-nfs-owner@vger.kernel.org List-ID: On Jul 22, 2015, at 5:14 PM, Trond Myklebust wrote: > On Wed, Jul 22, 2015 at 4:40 PM, Chuck Lever wrote: >> Hi Trond- >> >> >> On Jul 22, 2015, at 4:36 PM, Trond Myklebust wrote: >> >>> xprt_alloc_bc_request() cannot call xprt_free_bc_request() without >>> deadlocking, since it already holds the xprt->bc_pa_lock. >>> >>> Reported-by: Chuck Lever >>> Fixes: 0d2a970d0ae55 ("SUNRPC: Fix a backchannel race") >>> Signed-off-by: Trond Myklebust >> >> That?s exactly what I did as a basic fix, and I can report that >> it successfully avoids the deadlock. >> >> If xprt_alloc_bc_request() no longer calls xprt_free_bc_request(), >> are the accounting changes introduced by 0d2a970d0ae55 still >> necessary? > > The accounting changes are there to fix the race that Christoph > reported in which a valid backchannel request can be rejected by the > RPC layer if it happens to come in after the reply to the previous > request was sent, but before xprt_free_bc_request has completed. I > would therefore expect them still to be needed. > > That said, I just noticed that the bc_free_count was being incorrectly > maintained. Should be fixed with v2 of the patch series. I will get v2 in front of the tester who found this issue. -- Chuck Lever