From: Trond Myklebust Subject: Re: [PATCH 2/2] nfs: don't ignore return value from nfs_pageio_add_request Date: Wed, 19 Mar 2008 16:44:07 -0400 Message-ID: <1205959447.14710.3.camel@heimdal.trondhjem.org> References: <1205940280-10479-1-git-send-email-iisaman@citi.umich.edu> <1205940280-10479-2-git-send-email-iisaman@citi.umich.edu> <1205940280-10479-3-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]:32814 "EHLO pat.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934760AbYCSUoM (ORCPT ); Wed, 19 Mar 2008 16:44:12 -0400 In-Reply-To: <1205940280-10479-3-git-send-email-iisaman@citi.umich.edu> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, 2008-03-19 at 11:24 -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 > --- > fs/nfs/read.c | 5 ++++- > fs/nfs/write.c | 6 +++++- > 2 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/fs/nfs/read.c b/fs/nfs/read.c > index 3d7d963..77f8ac9 100644 > --- a/fs/nfs/read.c > +++ b/fs/nfs/read.c > @@ -533,7 +533,10 @@ readpage_async_filler(void *data, struct page *page) > > if (len < PAGE_CACHE_SIZE) > zero_user_segment(page, len, PAGE_CACHE_SIZE); > - nfs_pageio_add_request(desc->pgio, new); > + if (!nfs_pageio_add_request(desc->pgio, new)) { > + error = desc->pagio->pg_error; ^^^^^^^^^^^^^ this has never been compile-tested. > + goto out_unlock; > + } > return 0; > out_error: > error = PTR_ERR(new); > diff --git a/fs/nfs/write.c b/fs/nfs/write.c > index df85b7b..a146089 100644 > --- a/fs/nfs/write.c > +++ b/fs/nfs/write.c > @@ -39,6 +39,7 @@ static struct nfs_page * nfs_update_request(struct nfs_open_context*, > unsigned int, unsigned int); > static void nfs_pageio_init_write(struct nfs_pageio_descriptor *desc, > struct inode *inode, int ioflags); > +static void nfs_redirty_request(struct nfs_page *req); > static const struct rpc_call_ops nfs_write_partial_ops; > static const struct rpc_call_ops nfs_write_full_ops; > static const struct rpc_call_ops nfs_commit_ops; > @@ -288,7 +289,10 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio, > BUG(); > } > spin_unlock(&inode->i_lock); > - nfs_pageio_add_request(pgio, req); > + if (!nfs_pageio_add_request(pgio, req)) { > + nfs_redirty_request(req); Please could you reverse the order of these two patches. I'd like to send this one in for 2.6.25, but I can't do that as long as it depends on the previous patch. > + return pgio->pg_error; > + } > return 0; > } >