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authorAl Viro <viro@zeniv.linux.org.uk>2013-09-29 22:06:07 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2013-11-09 00:16:19 -0500
commit48a066e72d970a3e225a9c18690d570c736fc455 (patch)
tree9a1861c1be4309cf69964742d238eadd5d0b1832 /fs/namespace.c
parent42c326082d8a2c91506f951ace638deae1faf083 (diff)
RCU'd vfsmounts
* RCU-delayed freeing of vfsmounts * vfsmount_lock replaced with a seqlock (mount_lock) * sequence number from mount_lock is stored in nameidata->m_seq and used when we exit RCU mode * new vfsmount flag - MNT_SYNC_UMOUNT. Set by umount_tree() when its caller knows that vfsmount will have no surviving references. * synchronize_rcu() done between unlocking namespace_sem in namespace_unlock() and doing pending mntput(). * new helper: legitimize_mnt(mnt, seq). Checks the mount_lock sequence number against seq, then grabs reference to mnt. Then it rechecks mount_lock again to close the race and either returns success or drops the reference it has acquired. The subtle point is that in case of MNT_SYNC_UMOUNT we can simply decrement the refcount and sod off - aforementioned synchronize_rcu() makes sure that final mntput() won't come until we leave RCU mode. We need that, since we don't want to end up with some lazy pathwalk racing with umount() and stealing the final mntput() from it - caller of umount() may expect it to return only once the fs is shut down and we don't want to break that. In other cases (i.e. with MNT_SYNC_UMOUNT absent) we have to do full-blown mntput() in case of mount_lock sequence number mismatch happening just as we'd grabbed the reference, but in those cases we won't be stealing the final mntput() from anything that would care. * mntput_no_expire() doesn't lock anything on the fast path now. Incidentally, SMP and UP cases are handled the same way - no ifdefs there. * normal pathname resolution does *not* do any writes to mount_lock. It does, of course, bump the refcounts of vfsmount and dentry in the very end, but that's it. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/namespace.c')
-rw-r--r--fs/namespace.c135
1 files changed, 87 insertions, 48 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 500202ce10db..ac2ce8a766e1 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -53,7 +53,7 @@ EXPORT_SYMBOL_GPL(fs_kobj);
* It should be taken for write in all cases where the vfsmount
* tree or hash is modified or when a vfsmount structure is modified.
*/
-DEFINE_BRLOCK(vfsmount_lock);
+__cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
@@ -547,16 +547,38 @@ static void free_vfsmnt(struct mount *mnt)
kmem_cache_free(mnt_cache, mnt);
}
+/* call under rcu_read_lock */
+bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
+{
+ struct mount *mnt;
+ if (read_seqretry(&mount_lock, seq))
+ return false;
+ if (bastard == NULL)
+ return true;
+ mnt = real_mount(bastard);
+ mnt_add_count(mnt, 1);
+ if (likely(!read_seqretry(&mount_lock, seq)))
+ return true;
+ if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
+ mnt_add_count(mnt, -1);
+ return false;
+ }
+ rcu_read_unlock();
+ mntput(bastard);
+ rcu_read_lock();
+ return false;
+}
+
/*
* find the first mount at @dentry on vfsmount @mnt.
- * vfsmount_lock must be held for read or write.
+ * call under rcu_read_lock()
*/
struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
{
struct list_head *head = mount_hashtable + hash(mnt, dentry);
struct mount *p;
- list_for_each_entry(p, head, mnt_hash)
+ list_for_each_entry_rcu(p, head, mnt_hash)
if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
return p;
return NULL;
@@ -564,7 +586,7 @@ struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
/*
* find the last mount at @dentry on vfsmount @mnt.
- * vfsmount_lock must be held for read or write.
+ * mount_lock must be held.
*/
struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
{
@@ -596,17 +618,17 @@ struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
struct vfsmount *lookup_mnt(struct path *path)
{
struct mount *child_mnt;
+ struct vfsmount *m;
+ unsigned seq;
- br_read_lock(&vfsmount_lock);
- child_mnt = __lookup_mnt(path->mnt, path->dentry);
- if (child_mnt) {
- mnt_add_count(child_mnt, 1);
- br_read_unlock(&vfsmount_lock);
- return &child_mnt->mnt;
- } else {
- br_read_unlock(&vfsmount_lock);
- return NULL;
- }
+ rcu_read_lock();
+ do {
+ seq = read_seqbegin(&mount_lock);
+ child_mnt = __lookup_mnt(path->mnt, path->dentry);
+ m = child_mnt ? &child_mnt->mnt : NULL;
+ } while (!legitimize_mnt(m, seq));
+ rcu_read_unlock();
+ return m;
}
static struct mountpoint *new_mountpoint(struct dentry *dentry)
@@ -874,38 +896,46 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
return ERR_PTR(err);
}
+static void delayed_free(struct rcu_head *head)
+{
+ struct mount *mnt = container_of(head, struct mount, mnt_rcu);
+ kfree(mnt->mnt_devname);
+#ifdef CONFIG_SMP
+ free_percpu(mnt->mnt_pcp);
+#endif
+ kmem_cache_free(mnt_cache, mnt);
+}
+
static void mntput_no_expire(struct mount *mnt)
{
put_again:
-#ifdef CONFIG_SMP
- br_read_lock(&vfsmount_lock);
- if (likely(mnt->mnt_ns)) {
- /* shouldn't be the last one */
- mnt_add_count(mnt, -1);
- br_read_unlock(&vfsmount_lock);
+ rcu_read_lock();
+ mnt_add_count(mnt, -1);
+ if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
+ rcu_read_unlock();
return;
}
- br_read_unlock(&vfsmount_lock);
-
lock_mount_hash();
- mnt_add_count(mnt, -1);
if (mnt_get_count(mnt)) {
+ rcu_read_unlock();
unlock_mount_hash();
return;
}
-#else
- mnt_add_count(mnt, -1);
- if (likely(mnt_get_count(mnt)))
- return;
- lock_mount_hash();
-#endif
if (unlikely(mnt->mnt_pinned)) {
mnt_add_count(mnt, mnt->mnt_pinned + 1);
mnt->mnt_pinned = 0;
+ rcu_read_unlock();
unlock_mount_hash();
acct_auto_close_mnt(&mnt->mnt);
goto put_again;
}
+ if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
+ rcu_read_unlock();
+ unlock_mount_hash();
+ return;
+ }
+ mnt->mnt.mnt_flags |= MNT_DOOMED;
+ rcu_read_unlock();
list_del(&mnt->mnt_instance);
unlock_mount_hash();
@@ -924,7 +954,8 @@ put_again:
fsnotify_vfsmount_delete(&mnt->mnt);
dput(mnt->mnt.mnt_root);
deactivate_super(mnt->mnt.mnt_sb);
- free_vfsmnt(mnt);
+ mnt_free_id(mnt);
+ call_rcu(&mnt->mnt_rcu, delayed_free);
}
void mntput(struct vfsmount *mnt)
@@ -1137,6 +1168,8 @@ static void namespace_unlock(void)
list_splice_init(&unmounted, &head);
up_write(&namespace_sem);
+ synchronize_rcu();
+
while (!list_empty(&head)) {
mnt = list_first_entry(&head, struct mount, mnt_hash);
list_del_init(&mnt->mnt_hash);
@@ -1152,10 +1185,13 @@ static inline void namespace_lock(void)
}
/*
- * vfsmount lock must be held for write
+ * mount_lock must be held
* namespace_sem must be held for write
+ * how = 0 => just this tree, don't propagate
+ * how = 1 => propagate; we know that nobody else has reference to any victims
+ * how = 2 => lazy umount
*/
-void umount_tree(struct mount *mnt, int propagate)
+void umount_tree(struct mount *mnt, int how)
{
LIST_HEAD(tmp_list);
struct mount *p;
@@ -1163,7 +1199,7 @@ void umount_tree(struct mount *mnt, int propagate)
for (p = mnt; p; p = next_mnt(p, mnt))
list_move(&p->mnt_hash, &tmp_list);
- if (propagate)
+ if (how)
propagate_umount(&tmp_list);
list_for_each_entry(p, &tmp_list, mnt_hash) {
@@ -1171,6 +1207,8 @@ void umount_tree(struct mount *mnt, int propagate)
list_del_init(&p->mnt_list);
__touch_mnt_namespace(p->mnt_ns);
p->mnt_ns = NULL;
+ if (how < 2)
+ p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
list_del_init(&p->mnt_child);
if (mnt_has_parent(p)) {
put_mountpoint(p->mnt_mp);
@@ -1262,14 +1300,18 @@ static int do_umount(struct mount *mnt, int flags)
lock_mount_hash();
event++;
- if (!(flags & MNT_DETACH))
- shrink_submounts(mnt);
-
- retval = -EBUSY;
- if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
+ if (flags & MNT_DETACH) {
if (!list_empty(&mnt->mnt_list))
- umount_tree(mnt, 1);
+ umount_tree(mnt, 2);
retval = 0;
+ } else {
+ shrink_submounts(mnt);
+ retval = -EBUSY;
+ if (!propagate_mount_busy(mnt, 2)) {
+ if (!list_empty(&mnt->mnt_list))
+ umount_tree(mnt, 1);
+ retval = 0;
+ }
}
unlock_mount_hash();
namespace_unlock();
@@ -1955,7 +1997,7 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
struct mount *parent;
int err;
- mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);
+ mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL | MNT_DOOMED | MNT_SYNC_UMOUNT);
mp = lock_mount(path);
if (IS_ERR(mp))
@@ -2172,7 +2214,7 @@ resume:
* process a list of expirable mountpoints with the intent of discarding any
* submounts of a specific parent mountpoint
*
- * vfsmount_lock must be held for write
+ * mount_lock must be held for write
*/
static void shrink_submounts(struct mount *mnt)
{
@@ -2558,7 +2600,7 @@ out_type:
/*
* Return true if path is reachable from root
*
- * namespace_sem or vfsmount_lock is held
+ * namespace_sem or mount_lock is held
*/
bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
const struct path *root)
@@ -2573,9 +2615,9 @@ bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
int path_is_under(struct path *path1, struct path *path2)
{
int res;
- br_read_lock(&vfsmount_lock);
+ read_seqlock_excl(&mount_lock);
res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
- br_read_unlock(&vfsmount_lock);
+ read_sequnlock_excl(&mount_lock);
return res;
}
EXPORT_SYMBOL(path_is_under);
@@ -2748,8 +2790,6 @@ void __init mnt_init(void)
for (u = 0; u < HASH_SIZE; u++)
INIT_LIST_HEAD(&mountpoint_hashtable[u]);
- br_lock_init(&vfsmount_lock);
-
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
@@ -2788,9 +2828,8 @@ void kern_unmount(struct vfsmount *mnt)
{
/* release long term mount so mount point can be released */
if (!IS_ERR_OR_NULL(mnt)) {
- lock_mount_hash();
real_mount(mnt)->mnt_ns = NULL;
- unlock_mount_hash();
+ synchronize_rcu(); /* yecchhh... */
mntput(mnt);
}
}