The patch titled
Subject: autofs4: allow RCU-walk to walk through autofs4
has been added to the -mm tree. Its filename is
autofs4-allow-rcu-walk-to-walk-through-autofs4.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/autofs4-allow-rcu-walk-to-walk-through-autofs4.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/autofs4-allow-rcu-walk-to-walk-through-autofs4.patch
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------------------------------------------------------
From: NeilBrown <neilb@xxxxxxx>
Subject: 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@xxxxxxx>
Reviewed-by: Ian Kent <raven@xxxxxxxxxx>
Tested-by: Ian Kent <raven@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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 -puN fs/autofs4/autofs_i.h~autofs4-allow-rcu-walk-to-walk-through-autofs4 fs/autofs4/autofs_i.h
--- a/fs/autofs4/autofs_i.h~autofs4-allow-rcu-walk-to-walk-through-autofs4
+++ a/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 -puN fs/autofs4/dev-ioctl.c~autofs4-allow-rcu-walk-to-walk-through-autofs4 fs/autofs4/dev-ioctl.c
--- a/fs/autofs4/dev-ioctl.c~autofs4-allow-rcu-walk-to-walk-through-autofs4
+++ a/fs/autofs4/dev-ioctl.c
@@ -450,7 +450,7 @@ static int autofs_dev_ioctl_requester(st
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 -puN fs/autofs4/expire.c~autofs4-allow-rcu-walk-to-walk-through-autofs4 fs/autofs4/expire.c
--- a/fs/autofs4/expire.c~autofs4-allow-rcu-walk-to-walk-through-autofs4
+++ a/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 *d
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 -puN fs/autofs4/root.c~autofs4-allow-rcu-walk-to-walk-through-autofs4 fs/autofs4/root.c
--- a/fs/autofs4/root.c~autofs4-allow-rcu-walk-to-walk-through-autofs4
+++ a/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_exp
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 den
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_automo
* 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_automo
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_automo
}
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 dentr
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
_
Patches currently in -mm which might be from neilb@xxxxxxx are
autofs4-allow-rcu-walk-to-walk-through-autofs4.patch
autofs4-factor-should_expire-out-of-autofs4_expire_indirect.patch
autofs4-make-autofs4_can_expire-idempotent.patch
autofs4-avoid-taking-fs_lock-during-rcu-walk.patch
autofs4-d_manage-should-return-eisdir-when-appropriate-in-rcu-walk-mode.patch
autofs-the-documentation-i-wanted-to-read.patch
linux-next.patch
--
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