Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755190AbbEKSK7 (ORCPT ); Mon, 11 May 2015 14:10:59 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:47633 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754929AbbEKSIb (ORCPT ); Mon, 11 May 2015 14:08:31 -0400 From: Al Viro To: Linus Torvalds Cc: Neil Brown , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v3 107/110] VFS/namei: make the use of touch_atime() in get_link() RCU-safe. Date: Mon, 11 May 2015 19:08:07 +0100 Message-Id: <1431367690-5223-107-git-send-email-viro@ZenIV.linux.org.uk> X-Mailer: git-send-email 1.7.7.6 In-Reply-To: <20150511180650.GA4147@ZenIV.linux.org.uk> References: <20150511180650.GA4147@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3932 Lines: 135 From: NeilBrown touch_atime is not RCU-safe, and so cannot be called on an RCU walk. However, in situations where RCU-walk makes a difference, the symlink will likely to accessed much more often than it is useful to update the atime. So split out the test of "Does the atime actually need to be updated" into atime_needs_update(), and have get_link() unlazy if it finds that it will need to do that update. Signed-off-by: NeilBrown Signed-off-by: Al Viro --- fs/inode.c | 30 +++++++++++++++++++++--------- fs/namei.c | 12 +++++++++--- include/linux/fs.h | 1 + 3 files changed, 31 insertions(+), 12 deletions(-) diff --git a/fs/inode.c b/fs/inode.c index 952fb48..e8d6268 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -1585,36 +1585,47 @@ static int update_time(struct inode *inode, struct timespec *time, int flags) * This function automatically handles read only file systems and media, * as well as the "noatime" flag and inode specific "noatime" markers. */ -void touch_atime(const struct path *path) +bool atime_needs_update(const struct path *path, struct inode *inode) { struct vfsmount *mnt = path->mnt; - struct inode *inode = d_inode(path->dentry); struct timespec now; if (inode->i_flags & S_NOATIME) - return; + return false; if (IS_NOATIME(inode)) - return; + return false; if ((inode->i_sb->s_flags & MS_NODIRATIME) && S_ISDIR(inode->i_mode)) - return; + return false; if (mnt->mnt_flags & MNT_NOATIME) - return; + return false; if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode)) - return; + return false; now = current_fs_time(inode->i_sb); if (!relatime_need_update(mnt, inode, now)) - return; + return false; if (timespec_equal(&inode->i_atime, &now)) + return false; + + return true; +} + +void touch_atime(const struct path *path) +{ + struct vfsmount *mnt = path->mnt; + struct inode *inode = d_inode(path->dentry); + struct timespec now; + + if (!atime_needs_update(path, inode)) return; if (!sb_start_write_trylock(inode->i_sb)) return; - if (__mnt_want_write(mnt)) + if (__mnt_want_write(mnt) != 0) goto skip_update; /* * File systems can error out when updating inodes if they need to @@ -1625,6 +1636,7 @@ void touch_atime(const struct path *path) * We may also fail on filesystems that have the ability to make parts * of the fs read only, e.g. subvolumes in Btrfs. */ + now = current_fs_time(inode->i_sb); update_time(inode, &now, S_ATIME); __mnt_drop_write(mnt); skip_update: diff --git a/fs/namei.c b/fs/namei.c index 4d6065d..9ef8c50 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -958,13 +958,19 @@ const char *get_link(struct nameidata *nd) int error; const char *res; - if (nd->flags & LOOKUP_RCU) { + if (!(nd->flags & LOOKUP_RCU)) { + touch_atime(&last->link); + } else if (atime_needs_update(&last->link, inode)) { if (unlikely(unlazy_walk(nd, NULL, 0))) return ERR_PTR(-ECHILD); + touch_atime(&last->link); } - cond_resched(); - touch_atime(&last->link); + _cond_resched(); + if (nd->flags & LOOKUP_RCU) { + if (unlikely(unlazy_walk(nd, NULL, 0))) + return ERR_PTR(-ECHILD); + } error = security_inode_follow_link(dentry, inode, nd->flags & LOOKUP_RCU); diff --git a/include/linux/fs.h b/include/linux/fs.h index 8f73851..1426c43 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1880,6 +1880,7 @@ enum file_time_flags { S_VERSION = 8, }; +extern bool atime_needs_update(const struct path *, struct inode *); extern void touch_atime(const struct path *); static inline void file_accessed(struct file *file) { -- 2.1.4 -- 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/