Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758695Ab3DBXNh (ORCPT ); Tue, 2 Apr 2013 19:13:37 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:32954 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932993Ab3DBWMS (ORCPT ); Tue, 2 Apr 2013 18:12:18 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Al Viro Subject: [ 041/124] Nest rename_lock inside vfsmount_lock Date: Tue, 2 Apr 2013 15:10:23 -0700 Message-Id: <20130402221108.985609296@linuxfoundation.org> X-Mailer: git-send-email 1.8.1.rc1.5.g7e0651a In-Reply-To: <20130402221104.163133110@linuxfoundation.org> References: <20130402221104.163133110@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3708 Lines: 125 3.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro commit 7ea600b5314529f9d1b9d6d3c41cb26fce6a7a4a upstream. ... lest we get livelocks between path_is_under() and d_path() and friends. The thing is, wrt fairness lglocks are more similar to rwsems than to rwlocks; it is possible to have thread B spin on attempt to take lock shared while thread A is already holding it shared, if B is on lower-numbered CPU than A and there's a thread C spinning on attempt to take the same lock exclusive. As the result, we need consistent ordering between vfsmount_lock (lglock) and rename_lock (seq_lock), even though everything that takes both is going to take vfsmount_lock only shared. Spotted-by: Brad Spengler Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- fs/dcache.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2552,7 +2552,6 @@ static int prepend_path(const struct pat bool slash = false; int error = 0; - br_read_lock(&vfsmount_lock); while (dentry != root->dentry || vfsmnt != root->mnt) { struct dentry * parent; @@ -2582,8 +2581,6 @@ static int prepend_path(const struct pat if (!error && !slash) error = prepend(buffer, buflen, "/", 1); -out: - br_read_unlock(&vfsmount_lock); return error; global_root: @@ -2600,7 +2597,7 @@ global_root: error = prepend(buffer, buflen, "/", 1); if (!error) error = is_mounted(vfsmnt) ? 1 : 2; - goto out; + return error; } /** @@ -2627,9 +2624,11 @@ char *__d_path(const struct path *path, int error; prepend(&res, &buflen, "\0", 1); + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); error = prepend_path(path, root, &res, &buflen); write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error < 0) return ERR_PTR(error); @@ -2646,9 +2645,11 @@ char *d_absolute_path(const struct path int error; prepend(&res, &buflen, "\0", 1); + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); error = prepend_path(path, &root, &res, &buflen); write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error > 1) error = -EINVAL; @@ -2712,11 +2713,13 @@ char *d_path(const struct path *path, ch return path->dentry->d_op->d_dname(path->dentry, buf, buflen); get_fs_root(current->fs, &root); + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); error = path_with_deleted(path, &root, &res, &buflen); + write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error < 0) res = ERR_PTR(error); - write_sequnlock(&rename_lock); path_put(&root); return res; } @@ -2871,6 +2874,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, b get_fs_root_and_pwd(current->fs, &root, &pwd); error = -ENOENT; + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); if (!d_unlinked(pwd.dentry)) { unsigned long len; @@ -2880,6 +2884,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, b prepend(&cwd, &buflen, "\0", 1); error = prepend_path(&pwd, &root, &cwd, &buflen); write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error < 0) goto out; @@ -2900,6 +2905,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, b } } else { write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); } out: -- 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/