Return-Path: Received: from mfbichi11.ns.itscom.net ([219.110.2.189]:44791 "EHLO mfbichi11.ns.itscom.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751498Ab1AMNbT (ORCPT ); Thu, 13 Jan 2011 08:31:19 -0500 From: "J. R. Okajima" Subject: Re: NFS root lockups with -next 20110113 To: Mark Brown Cc: Trond Myklebust , Santosh Shilimkar , Nick Piggin , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org In-Reply-To: <20110113120626.GB30351@opensource.wolfsonmicro.com> References: <20110113120626.GB30351@opensource.wolfsonmicro.com> Date: Thu, 13 Jan 2011 22:22:07 +0900 Message-ID: <8138.1294924927@jrobl> Sender: linux-nfs-owner@vger.kernel.org List-ID: Content-Type: text/plain MIME-Version: 1.0 Mark Brown: > With -next 20110113 I'm experiencing lockups shortly after userspace > starts when booting with my root filesystem on NFS, log below. I can > boot into /bin/sh but running real userspace triggers this very easily. > This was introduced sometime this week. > > I've not bisected or otherwise investigated much yet, but I do notice > code added recently by Nick in "fs: rcu-walk for path lookup" showing up > in the backtrace so including him in the CCs. This and a report from Santosh Shilimkar look like the same problem which I reported, and I am testing this patch. If you can, please try it too. Note: Of course this is not offcial fix. J. R. Okajima diff --git a/fs/namei.c b/fs/namei.c index 5bb7588..51d052f 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -480,6 +480,7 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry { struct fs_struct *fs = current->fs; struct dentry *parent = nd->path.dentry; + int isroot; BUG_ON(!(nd->flags & LOOKUP_RCU)); if (nd->root.mnt) { @@ -489,18 +490,22 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry goto err_root; } spin_lock(&parent->d_lock); - spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED); - if (!__d_rcu_to_refcount(dentry, nd->seq)) - goto err; + isroot = IS_ROOT(dentry); + if (!isroot) { + spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED); + if (!__d_rcu_to_refcount(dentry, nd->seq)) + goto err; + } /* * If the sequence check on the child dentry passed, then the child has * not been removed from its parent. This means the parent dentry must * be valid and able to take a reference at this point. */ - BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent); + BUG_ON(!isroot && dentry->d_parent != parent); BUG_ON(!parent->d_count); parent->d_count++; - spin_unlock(&dentry->d_lock); + if (!isroot) + spin_unlock(&dentry->d_lock); spin_unlock(&parent->d_lock); if (nd->root.mnt) { path_get(&nd->root); @@ -513,7 +518,8 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry nd->flags &= ~LOOKUP_RCU; return 0; err: - spin_unlock(&dentry->d_lock); + if (!isroot) + spin_unlock(&dentry->d_lock); spin_unlock(&parent->d_lock); err_root: if (nd->root.mnt)