Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263702AbTICGlT (ORCPT ); Wed, 3 Sep 2003 02:41:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263705AbTICGlS (ORCPT ); Wed, 3 Sep 2003 02:41:18 -0400 Received: from ns.virtualhost.dk ([195.184.98.160]:51156 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S263702AbTICGlK (ORCPT ); Wed, 3 Sep 2003 02:41:10 -0400 Date: Wed, 3 Sep 2003 08:40:57 +0200 From: Jens Axboe To: Tejun Huh Cc: linux-kernel@vger.kernel.org, B.Zolnierkiewicz@elka.pw.edu.pl Subject: Re: [PATCH] ide task_map_rq() preempt count imbalance Message-ID: <20030903064057.GA14833@suse.de> References: <20030903055257.GA31635@atj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030903055257.GA31635@atj.dyndns.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2940 Lines: 96 On Wed, Sep 03 2003, Tejun Huh wrote: > Hello, > > 2.5 kernel continued to fail on my test machine with a lot of > scheduling while atomic messages. The offending function was > include/linux/ide.h:task_sectors() which calls task_map_rq() followed > by process_that_request_first(), taskfile_{input|output}_data() and > task_unmap_rq(). > > static inline void *task_map_rq(struct request *rq, unsigned long *flags) > { > /* > * fs request > */ > if (rq->cbio) > return rq_map_buffer(rq, flags); > > /* > * task request > */ > return rq->buffer + blk_rq_offset(rq); > } > > static inline void task_unmap_rq(struct request *rq, char *buffer, unsigned long *flags) > { > if (rq->cbio) > rq_unmap_buffer(buffer, flags); > } > > rq_[un]map_buffer() eventually call into k[un]map_atomic() which > adjust preempt_count(). The problem is that rq->cbio is cleared by > process_that_request_first() before calling task_unmap_rq(), so the > preempt_count() isn't decremented properly. > > As it seems that rq->cbio test is to avoid the cost of calling into > k[un]map_atomic, I just removed the optimization and it worked for me. > > I'm not familiar with ide and block layer. If I got something wrong, > please point out. > > -- > tejun > > # This is a BitKeeper generated patch for the following project: > # Project Name: Linux kernel tree > # This patch format is intended for GNU patch command version 2.5 or higher. > # This patch includes the following deltas: > # ChangeSet 1.1412 -> 1.1413 > # include/linux/ide.h 1.72 -> 1.73 > # > # The following is the BitKeeper ChangeSet Log > # -------------------------------------------- > # 03/09/03 tj@atj.dyndns.org 1.1413 > # - task_[un]map_rq() preempt count imbalance fixed. > # -------------------------------------------- > # > diff -Nru a/include/linux/ide.h b/include/linux/ide.h > --- a/include/linux/ide.h Wed Sep 3 14:50:20 2003 > +++ b/include/linux/ide.h Wed Sep 3 14:50:20 2003 > @@ -853,22 +853,12 @@ > > static inline void *task_map_rq(struct request *rq, unsigned long *flags) > { > - /* > - * fs request > - */ > - if (rq->cbio) > - return rq_map_buffer(rq, flags); > - > - /* > - * task request > - */ > - return rq->buffer + blk_rq_offset(rq); > + return rq_map_buffer(rq, flags); > } > > static inline void task_unmap_rq(struct request *rq, char *buffer, unsigned long *flags) > { > - if (rq->cbio) > - rq_unmap_buffer(buffer, flags); > + rq_unmap_buffer(buffer, flags); > } > > #endif /* !CONFIG_IDE_TASKFILE_IO */ This doesn't work, it's perfectly legit to use task_map_rq() on a non-bio backed request. You need to fix this differently. -- Jens Axboe - 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/