From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH scsi-misc-2.6 01/04] scsi: make scsi_send_eh_cmnd use its own timer instead of scmd->eh_timeout Date: Mon, 25 Apr 2005 08:46:11 +0900 Message-ID: <426C2FC3.4090105@gmail.com> References: <20050419143100.E231523D@htj.dyndns.org> <20050419143100.0F9A8C3B@htj.dyndns.org> <1114381342.4786.17.camel@mulgrave> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from rproxy.gmail.com ([64.233.170.201]:60372 "EHLO rproxy.gmail.com") by vger.kernel.org with ESMTP id S262483AbVDXXqR (ORCPT ); Sun, 24 Apr 2005 19:46:17 -0400 Received: by rproxy.gmail.com with SMTP id a41so823331rng for ; Sun, 24 Apr 2005 16:46:16 -0700 (PDT) In-Reply-To: <1114381342.4786.17.camel@mulgrave> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: SCSI Mailing List , Linux Kernel Hi, James. James Bottomley wrote: > On Tue, 2005-04-19 at 23:31 +0900, Tejun Heo wrote: > >> scmd->eh_timeout is used to resolve the race between command >> completion and timeout. However, during error handling, >> scsi_send_eh_cmnd uses scmd->eh_timeout. This creates a race >> condition between eh and normal completion for a request which >> has timed out and in the process of error handling. If the >> request completes while scmd->eh_timeout is being used by eh, >> eh timeout is lost and the command will be handled by both eh >> and completion path. This patch fixes the race by making >> scsi_send_eh_cmnd() use its own timer. >> >> This patch adds shost->eh_timeout field. The name of the >> field equals scmd->eh_timeout which is used for normal command >> timeout. As this can be confusing, renaming scmd->eh_timeout >> to something like scmd->cmd_timeout would be good. >> >> Reworked such that timeout race window is kept at minimal >> level as pointed out by James Bottomley. > > > This looks fine in principle. However, three comments > > 1. If you're doing this, there's no further use for eh_timeout, so > remove it (and preferably fix gdth_proc.c; however, it's better to break > the compile of that driver than have it rely on a now defunct field). If you're talking about scmd->eh_timeout, it's our main timer for normal command timeouts. If you're suggesting renaming it to something more apparant, I agree. Maybe just scmd->timeout will do. > 2. Use of eh_action is private to scsi_error.c, so you don't need to add > a new field to the host, just make eh_action a pointer to a private > eh_action structure which contains the timer and the semaphore. Sure. > 3. To close a really tiny window where the running timer could race with > the del_timer, it should probably be del_timer_sync(). The practical > effect of this is nil, but it would be correct programming. Sorry, but, AFAICT, that wouldn't close any window. We use timer pending for tie-breaker. When scsi_eh_done() wins, timer never gets to run, and if scsi_eh_times_out() wins, the eh thread is woken up only after the last reference to the timer/eh is finished (up operation). If I'm missing something, please point out. BTW, are you still keeping the bk tree up-to-date? And, if so, until when are you gonna keep the bk tree? I'm painfully trying to follow and convert all my trees to git, but I _really_ miss changeset browsing of bk. Call me lazy but it was just too nice browsing the changesets only with mouse. One way or the other, it's a shame. Thanks. -- tejun