Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756755AbaGIXmO (ORCPT ); Wed, 9 Jul 2014 19:42:14 -0400 Received: from cantor2.suse.de ([195.135.220.15]:54059 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756328AbaGIXmK (ORCPT ); Wed, 9 Jul 2014 19:42:10 -0400 From: NeilBrown To: Ian Kent Date: Thu, 10 Jul 2014 09:41:14 +1000 Subject: [PATCH 3/6] autofs4: allow RCU-walk to walk through autofs4. Cc: autofs@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <20140709234114.4525.46882.stgit@notabene.brown> In-Reply-To: <20140709233541.4525.25151.stgit@notabene.brown> References: <20140709233541.4525.25151.stgit@notabene.brown> User-Agent: StGit/0.16 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Any attempt to look up a pathname that passes though an autofs4 mount is currently forced out of RCU-walk into REF-walk. This can significantly hurt performance of many-thread work loads on many-core systems, especially if the automounted filesystem supports RCU-walk but doesn't get to benefit from it. So if autofs4_d_manage is called with rcu_walk set, only fail with -ECHILD if it is necessary to wait longer than a spinlock, and avoid even the spinlock in one trivial case. Signed-off-by: NeilBrown --- fs/autofs4/autofs_i.h | 2 +- fs/autofs4/dev-ioctl.c | 2 +- fs/autofs4/expire.c | 4 +++- fs/autofs4/root.c | 44 +++++++++++++++++++++++++++++--------------- 4 files changed, 34 insertions(+), 18 deletions(-) diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index 22a280151e45..99dbb05d6148 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -148,7 +148,7 @@ void autofs4_free_ino(struct autofs_info *); /* Expiration */ int is_autofs4_dentry(struct dentry *); -int autofs4_expire_wait(struct dentry *dentry); +int autofs4_expire_wait(struct dentry *dentry, int rcu_walk); int autofs4_expire_run(struct super_block *, struct vfsmount *, struct autofs_sb_info *, struct autofs_packet_expire __user *); diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c index 5b570b6efa28..aaf96cb25452 100644 --- a/fs/autofs4/dev-ioctl.c +++ b/fs/autofs4/dev-ioctl.c @@ -450,7 +450,7 @@ static int autofs_dev_ioctl_requester(struct file *fp, ino = autofs4_dentry_ino(path.dentry); if (ino) { err = 0; - autofs4_expire_wait(path.dentry); + autofs4_expire_wait(path.dentry, 0); spin_lock(&sbi->fs_lock); param->requester.uid = from_kuid_munged(current_user_ns(), ino->uid); param->requester.gid = from_kgid_munged(current_user_ns(), ino->gid); diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c index a7be57e39be7..7e2f22ce6954 100644 --- a/fs/autofs4/expire.c +++ b/fs/autofs4/expire.c @@ -467,7 +467,7 @@ found: return expired; } -int autofs4_expire_wait(struct dentry *dentry) +int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) { struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb); struct autofs_info *ino = autofs4_dentry_ino(dentry); @@ -477,6 +477,8 @@ int autofs4_expire_wait(struct dentry *dentry) spin_lock(&sbi->fs_lock); if (ino->flags & AUTOFS_INF_EXPIRING) { spin_unlock(&sbi->fs_lock); + if (rcu_walk) + return -ECHILD; DPRINTK("waiting for expire %p name=%.*s", dentry, dentry->d_name.len, dentry->d_name.name); diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c index cc87c1abac97..1ad119407e2f 100644 --- a/fs/autofs4/root.c +++ b/fs/autofs4/root.c @@ -208,7 +208,8 @@ next: return NULL; } -static struct dentry *autofs4_lookup_expiring(struct dentry *dentry) +static struct dentry *autofs4_lookup_expiring(struct dentry *dentry, + bool rcu_walk) { struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb); struct dentry *parent = dentry->d_parent; @@ -225,6 +226,11 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry) struct dentry *expiring; struct qstr *qstr; + if (rcu_walk) { + spin_unlock(&sbi->lookup_lock); + return ERR_PTR(-ECHILD); + } + ino = list_entry(p, struct autofs_info, expiring); expiring = ino->dentry; @@ -260,13 +266,15 @@ next: return NULL; } -static int autofs4_mount_wait(struct dentry *dentry) +static int autofs4_mount_wait(struct dentry *dentry, bool rcu_walk) { struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb); struct autofs_info *ino = autofs4_dentry_ino(dentry); int status = 0; if (ino->flags & AUTOFS_INF_PENDING) { + if (rcu_walk) + return -ECHILD; DPRINTK("waiting for mount name=%.*s", dentry->d_name.len, dentry->d_name.name); status = autofs4_wait(sbi, dentry, NFY_MOUNT); @@ -276,20 +284,22 @@ static int autofs4_mount_wait(struct dentry *dentry) return status; } -static int do_expire_wait(struct dentry *dentry) +static int do_expire_wait(struct dentry *dentry, bool rcu_walk) { struct dentry *expiring; - expiring = autofs4_lookup_expiring(dentry); + expiring = autofs4_lookup_expiring(dentry, rcu_walk); + if (IS_ERR(expiring)) + return PTR_ERR(expiring); if (!expiring) - return autofs4_expire_wait(dentry); + return autofs4_expire_wait(dentry, rcu_walk); else { /* * If we are racing with expire the request might not * be quite complete, but the directory has been removed * so it must have been successful, just wait for it. */ - autofs4_expire_wait(expiring); + autofs4_expire_wait(expiring, 0); autofs4_del_expiring(expiring); dput(expiring); } @@ -341,7 +351,7 @@ static struct vfsmount *autofs4_d_automount(struct path *path) * and the directory was removed, so just go ahead and try * the mount. */ - status = do_expire_wait(dentry); + status = do_expire_wait(dentry, 0); if (status && status != -EAGAIN) return NULL; @@ -349,7 +359,7 @@ static struct vfsmount *autofs4_d_automount(struct path *path) spin_lock(&sbi->fs_lock); if (ino->flags & AUTOFS_INF_PENDING) { spin_unlock(&sbi->fs_lock); - status = autofs4_mount_wait(dentry); + status = autofs4_mount_wait(dentry, 0); if (status) return ERR_PTR(status); goto done; @@ -390,7 +400,7 @@ static struct vfsmount *autofs4_d_automount(struct path *path) } ino->flags |= AUTOFS_INF_PENDING; spin_unlock(&sbi->fs_lock); - status = autofs4_mount_wait(dentry); + status = autofs4_mount_wait(dentry, 0); spin_lock(&sbi->fs_lock); ino->flags &= ~AUTOFS_INF_PENDING; if (status) { @@ -426,21 +436,25 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk) return 0; } - /* We need to sleep, so we need pathwalk to be in ref-mode */ - if (rcu_walk) - return -ECHILD; - /* Wait for pending expires */ - do_expire_wait(dentry); + if (do_expire_wait(dentry, rcu_walk) == -ECHILD) + return -ECHILD; /* * This dentry may be under construction so wait on mount * completion. */ - status = autofs4_mount_wait(dentry); + status = autofs4_mount_wait(dentry, rcu_walk); if (status) return status; + if (rcu_walk) + /* No need to consider returning -EISDIR as + * there is no risk that ->d_automount will + * be called + */ + return status; + spin_lock(&sbi->fs_lock); /* * If the dentry has been selected for expire while we slept -- 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/