autofs races

* 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>

3 files changed, 15 insertions, 22 deletions

diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index f0d268b97d19..a439548de785 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -70,9 +70,13 @@ struct autofs_info {
 };
 
 #define AUTOFS_INF_EXPIRING     (1<<0) /* dentry 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 */
 
diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 9510d8d2e9cd..b493909e7492 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -316,19 +316,17 @@ struct dentry *autofs4_expire_direct(struct super_block *sb,
         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);
@@ -446,7 +444,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
         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);
@@ -455,7 +453,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
                         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);
@@ -465,7 +463,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
                         goto found;
                 }
 
-                ino->flags &= ~AUTOFS_INF_NO_RCU;
+                ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;
                 if (expired != dentry)
                         dput(expired);
                 spin_unlock(&sbi->fs_lock);
@@ -475,17 +473,8 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
 found:
         pr_debug("returning %p %pd\n", 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;
 }
 
@@ -496,7 +485,7 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk)
         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;
@@ -554,7 +543,7 @@ int autofs4_expire_run(struct super_block *sb,
         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);
 
@@ -583,7 +572,7 @@ int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
                 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);
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 78bd80298528..3767f6641af1 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -458,7 +458,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
                  */
                 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;