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Message-ID: <20080718023717.12802.80763.stgit@raven.themaw.net>
Date: Fri, 18 Jul 2008 10:37:18 +0800
From: Ian Kent <raven@...maw.net>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: autofs mailing list <autofs@...ux.kernel.org>,
Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
Al Viro <viro@...IV.linux.org.uk>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4/7] autofs4 - fix indirect mount pending expire race
The selection of a dentry for expiration and the setting of the
AUTOFS_INF_EXPIRING flag isn't done atomically which can lead to
lookups walking into an expiring mount.
What happens is that an expire is initiated by the daemon and
a dentry is selected for expire but, since there is no lock
held between the selection and setting of the expiring flag,
a process may find the flag clear and continue walking into
the mount tree at the same time the daemon attempts the expire
it.
Signed-off-by: Ian Kent <raven@...maw.net>
---
fs/autofs4/autofs_i.h | 10 +++-------
fs/autofs4/expire.c | 46 +++++++++++++++++++++++++++++++++++-----------
fs/autofs4/root.c | 32 +++++++++++++++++++++++++++-----
3 files changed, 65 insertions(+), 23 deletions(-)
diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index 058e180..5d90ed3 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -138,18 +138,14 @@ static inline int autofs4_oz_mode(struct autofs_sb_info *sbi) {
static inline int autofs4_ispending(struct dentry *dentry)
{
struct autofs_info *inf = autofs4_dentry_ino(dentry);
- int pending = 0;
if (dentry->d_flags & DCACHE_AUTOFS_PENDING)
return 1;
- if (inf) {
- spin_lock(&inf->sbi->fs_lock);
- pending = inf->flags & AUTOFS_INF_EXPIRING;
- spin_unlock(&inf->sbi->fs_lock);
- }
+ if (inf->flags & AUTOFS_INF_EXPIRING)
+ return 1;
- return pending;
+ return 0;
}
static inline void autofs4_copy_atime(struct file *src, struct file *dst)
diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 894fee5..19f5bea 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -292,6 +292,8 @@ static struct dentry *autofs4_expire_indirect(struct super_block *sb,
struct list_head *next;
int do_now = how & AUTOFS_EXP_IMMEDIATE;
int exp_leaves = how & AUTOFS_EXP_LEAVES;
+ struct autofs_info *ino;
+ unsigned int ino_count;
if (!root)
return NULL;
@@ -316,6 +318,9 @@ static struct dentry *autofs4_expire_indirect(struct super_block *sb,
dentry = dget(dentry);
spin_unlock(&dcache_lock);
+ spin_lock(&sbi->fs_lock);
+ ino = autofs4_dentry_ino(dentry);
+
/*
* Case 1: (i) indirect mount or top level pseudo direct mount
* (autofs-4.1).
@@ -326,6 +331,11 @@ static struct dentry *autofs4_expire_indirect(struct super_block *sb,
DPRINTK("checking mountpoint %p %.*s",
dentry, (int)dentry->d_name.len, dentry->d_name.name);
+ /* Path walk currently on this dentry? */
+ ino_count = atomic_read(&ino->count) + 2;
+ if (atomic_read(&dentry->d_count) > ino_count)
+ goto next;
+
/* Can we umount this guy */
if (autofs4_mount_busy(mnt, dentry))
goto next;
@@ -343,23 +353,25 @@ static struct dentry *autofs4_expire_indirect(struct super_block *sb,
/* Case 2: tree mount, expire iff entire tree is not busy */
if (!exp_leaves) {
- /* Lock the tree as we must expire as a whole */
- spin_lock(&sbi->fs_lock);
- if (!autofs4_tree_busy(mnt, dentry, timeout, do_now)) {
- struct autofs_info *inf = autofs4_dentry_ino(dentry);
+ /* Path walk currently on this dentry? */
+ ino_count = atomic_read(&ino->count) + 1;
+ if (atomic_read(&dentry->d_count) > ino_count)
+ goto next;
- /* Set this flag early to catch sys_chdir and the like */
- inf->flags |= AUTOFS_INF_EXPIRING;
- spin_unlock(&sbi->fs_lock);
+ if (!autofs4_tree_busy(mnt, dentry, timeout, do_now)) {
expired = dentry;
goto found;
}
- spin_unlock(&sbi->fs_lock);
/*
* Case 3: pseudo direct mount, expire individual leaves
* (autofs-4.1).
*/
} else {
+ /* Path walk currently on this dentry? */
+ ino_count = atomic_read(&ino->count) + 1;
+ if (atomic_read(&dentry->d_count) > ino_count)
+ goto next;
+
expired = autofs4_check_leaves(mnt, dentry, timeout, do_now);
if (expired) {
dput(dentry);
@@ -367,6 +379,7 @@ static struct dentry *autofs4_expire_indirect(struct super_block *sb,
}
}
next:
+ spin_unlock(&sbi->fs_lock);
dput(dentry);
spin_lock(&dcache_lock);
next = next->next;
@@ -377,6 +390,9 @@ next:
found:
DPRINTK("returning %p %.*s",
expired, (int)expired->d_name.len, expired->d_name.name);
+ ino = autofs4_dentry_ino(expired);
+ ino->flags |= AUTOFS_INF_EXPIRING;
+ spin_unlock(&sbi->fs_lock);
spin_lock(&dcache_lock);
list_move(&expired->d_parent->d_subdirs, &expired->d_u.d_child);
spin_unlock(&dcache_lock);
@@ -390,7 +406,9 @@ int autofs4_expire_run(struct super_block *sb,
struct autofs_packet_expire __user *pkt_p)
{
struct autofs_packet_expire pkt;
+ struct autofs_info *ino;
struct dentry *dentry;
+ int ret = 0;
memset(&pkt,0,sizeof pkt);
@@ -406,9 +424,14 @@ int autofs4_expire_run(struct super_block *sb,
dput(dentry);
if ( copy_to_user(pkt_p, &pkt, sizeof(struct autofs_packet_expire)) )
- return -EFAULT;
+ ret = -EFAULT;
- return 0;
+ spin_lock(&sbi->fs_lock);
+ ino = autofs4_dentry_ino(dentry);
+ ino->flags &= ~AUTOFS_INF_EXPIRING;
+ spin_unlock(&sbi->fs_lock);
+
+ return ret;
}
/* Call repeatedly until it returns -EAGAIN, meaning there's nothing
@@ -433,9 +456,10 @@ int autofs4_expire_multi(struct super_block *sb, struct vfsmount *mnt,
/* This is synchronous because it makes the daemon a
little easier */
- ino->flags |= AUTOFS_INF_EXPIRING;
ret = autofs4_wait(sbi, dentry, NFY_EXPIRE);
+ spin_lock(&sbi->fs_lock);
ino->flags &= ~AUTOFS_INF_EXPIRING;
+ spin_unlock(&sbi->fs_lock);
dput(dentry);
}
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 2944b28..2ed2a51 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -133,7 +133,10 @@ static int try_to_fill_dentry(struct dentry *dentry, int flags)
/* Block on any pending expiry here; invalidate the dentry
when expiration is done to trigger mount request with a new
dentry */
- if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
+ spin_lock(&sbi->fs_lock);
+ if (ino->flags & AUTOFS_INF_EXPIRING) {
+ spin_unlock(&sbi->fs_lock);
+
DPRINTK("waiting for expire %p name=%.*s",
dentry, dentry->d_name.len, dentry->d_name.name);
@@ -149,8 +152,11 @@ static int try_to_fill_dentry(struct dentry *dentry, int flags)
status = d_invalidate(dentry);
if (status != -EBUSY)
return -EAGAIN;
- }
+ goto cont;
+ }
+ spin_unlock(&sbi->fs_lock);
+cont:
DPRINTK("dentry=%p %.*s ino=%p",
dentry, dentry->d_name.len, dentry->d_name.name, dentry->d_inode);
@@ -229,15 +235,21 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
goto done;
/* If an expire request is pending wait for it. */
- if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
+ spin_lock(&sbi->fs_lock);
+ if (ino->flags & AUTOFS_INF_EXPIRING) {
+ spin_unlock(&sbi->fs_lock);
+
DPRINTK("waiting for active request %p name=%.*s",
dentry, dentry->d_name.len, dentry->d_name.name);
status = autofs4_wait(sbi, dentry, NFY_NONE);
DPRINTK("request done status=%d", status);
- }
+ goto cont;
+ }
+ spin_unlock(&sbi->fs_lock);
+cont:
/*
* If the dentry contains directories then it is an
* autofs multi-mount with no root mount offset. So
@@ -292,8 +304,11 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
int status = 1;
/* Pending dentry */
+ spin_lock(&sbi->fs_lock);
if (autofs4_ispending(dentry)) {
/* The daemon never causes a mount to trigger */
+ spin_unlock(&sbi->fs_lock);
+
if (oz_mode)
return 1;
@@ -316,6 +331,7 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
return status;
}
+ spin_unlock(&sbi->fs_lock);
/* Negative dentry.. invalidate if "old" */
if (dentry->d_inode == NULL)
@@ -329,6 +345,7 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
DPRINTK("dentry=%p %.*s, emptydir",
dentry, dentry->d_name.len, dentry->d_name.name);
spin_unlock(&dcache_lock);
+
/* The daemon never causes a mount to trigger */
if (oz_mode)
return 1;
@@ -521,13 +538,18 @@ static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, s
* so it must have been successful, so just wait for it.
*/
ino = autofs4_dentry_ino(expiring);
- while (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
+ spin_lock(&sbi->fs_lock);
+ if (ino->flags & AUTOFS_INF_EXPIRING) {
+ spin_unlock(&sbi->fs_lock);
DPRINTK("wait for incomplete expire %p name=%.*s",
expiring, expiring->d_name.len,
expiring->d_name.name);
autofs4_wait(sbi, expiring, NFY_NONE);
DPRINTK("request completed");
+ goto cont;
}
+ spin_unlock(&sbi->fs_lock);
+cont:
spin_lock(&sbi->lookup_lock);
if (!list_empty(&ino->expiring))
list_del_init(&ino->expiring);
--
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