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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>
This commit is contained in:
Al Viro 2016-06-12 11:24:46 -04:00
parent ba65dc5ef1
commit ea01a18494
3 changed files with 15 additions and 22 deletions
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8
fs/autofs4/autofs_i.h
View File

@ -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 */

27
fs/autofs4/expire.c
View File

@ -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);

2
fs/autofs4/root.c
View File

@ -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;