From: Trond Myklebust Subject: Re: [PATCH 2/2] nfs: don't ignore return value from nfs_pageio_add_request Date: Wed, 19 Mar 2008 10:50:39 -0400 Message-ID: <1205938239.8388.50.camel@heimdal.trondhjem.org> References: <1205936000-9336-1-git-send-email-iisaman@citi.umich.edu> <1205936000-9336-2-git-send-email-iisaman@citi.umich.edu> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-nfs@vger.kernel.org To: Fred Isaman Return-path: Received: from pat.uio.no ([129.240.10.15]:46066 "EHLO pat.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754568AbYCSTgh (ORCPT ); Wed, 19 Mar 2008 15:36:37 -0400 In-Reply-To: <1205936000-9336-2-git-send-email-iisaman@citi.umich.edu> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, 2008-03-19 at 10:13 -0400, Fred Isaman wrote: > Ignoring the return value from nfs_pageio_add_request can cause deadlocks. > > In read path: > call nfs_pageio_add_request from readpage_async_filler > assume at this point that there are requests already in desc, that > can't be merged with the current request. > so nfs_pageio_doio is fired up to clear out desc. > assume something goes wrong in setting up the io, so desc->pg_error is set. > This causes nfs_pageio_add_request to return 0, *WITHOUT* adding the original > request. > BUT, since return code is ignored, readpage_async_filler assumes it has > been added, and does nothing further, leaving page locked. > do_generic_mapping_read will eventually call lock_page, resulting in deadlock > > In write path: > page is marked dirty by generic_perform_write > nfs_writepages is called > call nfs_pageio_add_request from nfs_page_async_flush > assume at this point that there are requests already in desc, that > can't be merged with the current request. > so nfs_pageio_doio is fired up to clear out desc. > assume something goes wrong in setting up the io, so desc->pg_error is set. > This causes nfs_page_async_flush to return 0, *WITHOUT* adding the original > request, yet marking the request as locked (PG_BUSY) and in writeback, > clearing dirty marks. > The next time a write is done to the page, deadlock will result as > nfs_write_end calls nfs_update_request > > Signed-off-by: Fred Isaman Applied. Thanks Fred!