diff options
author | NeilBrown <neilb@suse.de> | 2014-10-13 22:52:14 (GMT) |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-10-14 00:18:16 (GMT) |
commit | 23bfc2a24ea3d993cc5cc90c9970654e7232502e (patch) | |
tree | a2bc0e834578b8b8559e255363e9b95d08158e97 /fs/autofs4/root.c | |
parent | 8a273345dcb1d74d12f28a0a76320b23e7e32f55 (diff) | |
download | linux-23bfc2a24ea3d993cc5cc90c9970654e7232502e.tar.xz |
autofs4: allow RCU-walk to walk through autofs4
This series teaches autofs about RCU-walk so that we don't drop straight
into REF-walk when we hit an autofs directory, and so that we avoid
spinlocks as much as possible when performing an RCU-walk.
This is needed so that the benefits of the recent NFS support for
RCU-walk are fully available when NFS filesystems are automounted.
Patches have been carefully reviewed and tested both with test suites
and in production - thanks a lot to Ian Kent for his support there.
This patch (of 6):
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.
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Ian Kent <raven@themaw.net>
Tested-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/autofs4/root.c')
-rw-r--r-- | fs/autofs4/root.c | 44 |
1 files changed, 29 insertions, 15 deletions
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c index cdb25eb..2296c83 100644 --- a/fs/autofs4/root.c +++ b/fs/autofs4/root.c @@ -210,7 +210,8 @@ 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; @@ -229,6 +230,11 @@ 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; @@ -264,13 +270,15 @@ 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); @@ -280,20 +288,22 @@ 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); } @@ -345,7 +355,7 @@ 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; @@ -353,7 +363,7 @@ 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; @@ -394,7 +404,7 @@ 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) { @@ -430,21 +440,25 @@ 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) + /* it is always safe to return 0 as the worst that + * will happen is we retry in REF-walk mode. + * Better than always taking a lock. + */ + return 0; + spin_lock(&sbi->fs_lock); /* * If the dentry has been selected for expire while we slept |