From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934906Ab3DGXb6 (ORCPT ); Sun, 7 Apr 2013 19:31:58 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:46798 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934776Ab3DGXbf (ORCPT ); Sun, 7 Apr 2013 19:31:35 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Al Viro" Date: Sun, 07 Apr 2013 23:45:42 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [31/74] Nest rename_lock inside vfsmount_lock In-Reply-To: X-SA-Exim-Connect-IP: 2001:470:1f08:1539:b4b3:7e2a:e2d0:3478 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.43-rc1 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 [bwh: Backported to 3.2: - Adjust context - s/&vfsmount_lock/vfsmount_lock/] Signed-off-by: Ben Hutchings --- fs/dcache.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2445,7 +2445,6 @@ 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; @@ -2475,8 +2474,6 @@ 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: @@ -2493,7 +2490,7 @@ global_root: error = prepend(buffer, buflen, "/", 1); if (!error) error = vfsmnt->mnt_ns ? 1 : 2; - goto out; + return error; } /** @@ -2520,9 +2517,11 @@ 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); @@ -2539,9 +2538,11 @@ 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; @@ -2605,11 +2606,13 @@ 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; } @@ -2764,6 +2767,7 @@ 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; @@ -2773,6 +2777,7 @@ 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; @@ -2793,6 +2798,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, b } } else { write_sequnlock(&rename_lock); + br_read_unlock(vfsmount_lock); } out: