[PATCH 4.4 44/73] autofs races

Greg Kroah-Hartman
2016-09-28T09:32:28Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit ea01a18494b3d7a91b2f1f2a6a5aaef4741bc294 upstream.

* make autofs4_expire_indirect() skip the dentries being in process of
expiry
* do *not* mess with list_move(); making sure that dentry with
AUTOFS_INF_EXPIRING are not picked for expiry is enough.
* do not remove NO_RCU when we set EXPIRING, don't bother with smp_mb()
there. Clear it at the same time we clear EXPIRING. Makes a bunch of
tests simpler.
* rename NO_RCU to WANT_EXPIRE, which is what it really is.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/autofs4/autofs_i.h | 8 ++++++--
fs/autofs4/expire.c | 27 ++++++++-------------------
fs/autofs4/root.c | 2 +-
3 files changed, 15 insertions(+), 22 deletions(-)

--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -79,9 +79,13 @@ struct autofs_info {
};

#define AUTOFS_INF_EXPIRING (1<<0) /* dentry is in the process of expiring */
-#define AUTOFS_INF_NO_RCU (1<<1) /* the dentry is being considered
+#define AUTOFS_INF_WANT_EXPIRE (1<<1) /* the dentry is being considered
* for expiry, so RCU_walk is
- * not permitted
+ * not permitted. If it progresses to
+ * actual expiry attempt, the flag is
+ * not cleared when EXPIRING is set -
+ * in that case it gets cleared only
+ * when it comes to clearing EXPIRING.
*/
#define AUTOFS_INF_PENDING (1<<2) /* dentry pending mount */

--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -315,19 +315,17 @@ struct dentry *autofs4_expire_direct(str
if (ino->flags & AUTOFS_INF_PENDING)
goto out;
if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
- ino->flags |= AUTOFS_INF_NO_RCU;
+ ino->flags |= AUTOFS_INF_WANT_EXPIRE;
spin_unlock(&sbi->fs_lock);
synchronize_rcu();
spin_lock(&sbi->fs_lock);
if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
ino->flags |= AUTOFS_INF_EXPIRING;
- smp_mb();
- ino->flags &= ~AUTOFS_INF_NO_RCU;
init_completion(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
return root;
}
- ino->flags &= ~AUTOFS_INF_NO_RCU;
+ ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;
}
out:
spin_unlock(&sbi->fs_lock);
@@ -444,7 +442,7 @@ struct dentry *autofs4_expire_indirect(s
while ((dentry = get_next_positive_subdir(dentry, root))) {
spin_lock(&sbi->fs_lock);
ino = autofs4_dentry_ino(dentry);
- if (ino->flags & AUTOFS_INF_NO_RCU)
+ if (ino->flags & AUTOFS_INF_WANT_EXPIRE)
expired = NULL;
else
expired = should_expire(dentry, mnt, timeout, how);
@@ -453,7 +451,7 @@ struct dentry *autofs4_expire_indirect(s
continue;
}
ino = autofs4_dentry_ino(expired);
- ino->flags |= AUTOFS_INF_NO_RCU;
+ ino->flags |= AUTOFS_INF_WANT_EXPIRE;
spin_unlock(&sbi->fs_lock);
synchronize_rcu();
spin_lock(&sbi->fs_lock);
@@ -463,7 +461,7 @@ struct dentry *autofs4_expire_indirect(s
goto found;
}

- ino->flags &= ~AUTOFS_INF_NO_RCU;
+ ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;
if (expired != dentry)
dput(expired);
spin_unlock(&sbi->fs_lock);
@@ -473,17 +471,8 @@ struct dentry *autofs4_expire_indirect(s
found:
DPRINTK("returning %p %pd", expired, expired);
ino->flags |= AUTOFS_INF_EXPIRING;
- smp_mb();
- ino->flags &= ~AUTOFS_INF_NO_RCU;
init_completion(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
- spin_lock(&sbi->lookup_lock);
- spin_lock(&expired->d_parent->d_lock);
- spin_lock_nested(&expired->d_lock, DENTRY_D_LOCK_NESTED);
- list_move(&expired->d_parent->d_subdirs, &expired->d_child);
- spin_unlock(&expired->d_lock);
- spin_unlock(&expired->d_parent->d_lock);
- spin_unlock(&sbi->lookup_lock);
return expired;
}

@@ -494,7 +483,7 @@ int autofs4_expire_wait(struct dentry *d
int status;

/* Block on any pending expire */
- if (!(ino->flags & (AUTOFS_INF_EXPIRING | AUTOFS_INF_NO_RCU)))
+ if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE))
return 0;
if (rcu_walk)
return -ECHILD;
@@ -551,7 +540,7 @@ int autofs4_expire_run(struct super_bloc
ino = autofs4_dentry_ino(dentry);
/* avoid rapid-fire expire attempts if expiry fails */
ino->last_used = now;
- ino->flags &= ~AUTOFS_INF_EXPIRING;
+ ino->flags &= ~(AUTOFS_INF_EXPIRING|AUTOFS_INF_WANT_EXPIRE);
complete_all(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);

@@ -579,7 +568,7 @@ int autofs4_do_expire_multi(struct super
spin_lock(&sbi->fs_lock);
/* avoid rapid-fire expire attempts if expiry fails */
ino->last_used = now;
- ino->flags &= ~AUTOFS_INF_EXPIRING;
+ ino->flags &= ~(AUTOFS_INF_EXPIRING|AUTOFS_INF_WANT_EXPIRE);
complete_all(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
dput(dentry);
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -455,7 +455,7 @@ static int autofs4_d_manage(struct dentr
* a mount-trap.
*/
struct inode *inode;
- if (ino->flags & (AUTOFS_INF_EXPIRING | AUTOFS_INF_NO_RCU))
+ if (ino->flags & AUTOFS_INF_WANT_EXPIRE)
return 0;
if (d_mountpoint(dentry))
return 0;