From mboxrd@z Thu Jan 1 00:00:00 1970 From: Trond Myklebust Subject: Re: [PATCH 10/12] NFS: Simplify nfs_wb_page() Date: Wed, 17 Mar 2010 13:58:02 -0400 Message-ID: <1268848682.8335.5.camel@localhost.localdomain> References: <20100125221544.16750.70574.stgit@localhost.localdomain> <20100125221545.16750.19154.stgit@localhost.localdomain> <16839.1268247109@jrobl> <1268249482.3096.76.camel@localhost.localdomain> <1268252300.3096.81.camel@localhost.localdomain> <22120.1268282756@jrobl> <1268317582.3354.9.camel@localhost.localdomain> <20100317164938.GA31415@infradead.org> <1268846819.8335.3.camel@localhost.localdomain> <20100317135205.58731824@tlielax.poochiereds.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Cc: Christoph Hellwig , "J. R. Okajima" , linux-nfs@vger.kernel.org, Wu Fengguang , Peter Zijlstra , Jan Kara , Steve Rago , Jens Axboe , Arjan van de Ven , Ingo Molnar , linux-fsdevel@vger.kernel.org, Christoph Hellwig , Al Viro To: Jeff Layton Return-path: Received: from mx2.netapp.com ([216.240.18.37]:16133 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754904Ab0CQR6z convert rfc822-to-8bit (ORCPT ); Wed, 17 Mar 2010 13:58:55 -0400 In-Reply-To: <20100317135205.58731824@tlielax.poochiereds.net> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 2010-03-17 at 13:52 -0400, Jeff Layton wrote: > On Wed, 17 Mar 2010 13:26:59 -0400 > Trond Myklebust wrote: > > > On Wed, 2010-03-17 at 12:49 -0400, Christoph Hellwig wrote: > > > On Thu, Mar 11, 2010 at 09:26:22AM -0500, Trond Myklebust wrote: > > > > @@ -112,12 +112,10 @@ void nfs_unlock_request(struct nfs_page *req) > > > > */ > > > > int nfs_set_page_tag_locked(struct nfs_page *req) > > > > { > > > > - struct nfs_inode *nfsi = NFS_I(req->wb_context->path.dentry->d_inode); > > > > - > > > > if (!nfs_lock_request_dontget(req)) > > > > return 0; > > > > if (req->wb_page != NULL) > > > > - radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED); > > > > + radix_tree_tag_set(&NFS_I(req->wb_context->path.dentry->d_inode)->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED); > > > > return 1; > > > > } > > > > > > > > > > This hunk is not only entirely unrealted to the fix, but also osbfucates > > > the code. > > > > > > > @@ -126,10 +124,10 @@ int nfs_set_page_tag_locked(struct nfs_page *req) > > > > */ > > > > void nfs_clear_page_tag_locked(struct nfs_page *req) > > > > { > > > > - struct inode *inode = req->wb_context->path.dentry->d_inode; > > > > - struct nfs_inode *nfsi = NFS_I(inode); > > > > - > > > > if (req->wb_page != NULL) { > > > > + struct inode *inode = req->wb_context->path.dentry->d_inode; > > > > + struct nfs_inode *nfsi = NFS_I(inode); > > > > + > > > > spin_lock(&inode->i_lock); > > > > radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED); > > > > nfs_unlock_request(req); > > > > > > Another one unrelated to the fix. > > > > > > > No. They are needed because we don't want to dereference req->wb_context > > after it (and req->wb_page) have been cleared. Without these 2 hunks, > > the resulting kernel Oopses. > > > > It seems like that just tightens up the race window without actually > closing it. > > Just because wb_page was non-NULL when you checked it gives no > guarantee that wb_context won't be NULL when you go to dereference it, > right? > The above 2 functions are the ones that lock and unlock the request. Once locked by means of the call to nfs_lock_request_dontget(req), no other threads can change the contents of wb_page and wb_context. IOW: yes, there is definitely such a guarantee... Trond