fs: brlock vfsmount_lock
fs: brlock vfsmount_lock
Use a brlock for the vfsmount lock. It must be taken for write whenever
modifying the mount hash or associated fields, and may be taken for read when
performing mount hash lookups.
A new lock is added for the mnt-id allocator, so it doesn't need to take
the heavy vfsmount write-lock.
The number of atomics should remain the same for fastpath rlock cases, though
code would be slightly slower due to per-cpu access. Scalability is not not be
much improved in common cases yet, due to other locks (ie. dcache_lock) getting
in the way. However path lookups crossing mountpoints should be one case where
scalability is improved (currently requiring the global lock).
The slowpath is slower due to use of brlock. On a 64 core, 64 socket, 32 node
Altix system (high latency to remote nodes), a simple umount microbenchmark
(mount --bind mnt mnt2 ; umount mnt2 loop 1000 times), before this patch it
took 6.8s, afterwards took 7.1s, about 5% slower.
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index 2e10cb1..de402eb 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -11,6 +11,8 @@
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/percpu.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/kernel.h>
@@ -38,12 +40,10 @@
#define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head))
#define HASH_SIZE (1UL << HASH_SHIFT)
-/* spinlock for vfsmount related operations, inplace of dcache_lock */
-__cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
-
static int event;
static DEFINE_IDA(mnt_id_ida);
static DEFINE_IDA(mnt_group_ida);
+static DEFINE_SPINLOCK(mnt_id_lock);
static int mnt_id_start = 0;
static int mnt_group_start = 1;
@@ -55,6 +55,16 @@
struct kobject *fs_kobj;
EXPORT_SYMBOL_GPL(fs_kobj);
+/*
+ * vfsmount lock may be taken for read to prevent changes to the
+ * vfsmount hash, ie. during mountpoint lookups or walking back
+ * up the tree.
+ *
+ * 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);
+
static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
@@ -65,18 +75,21 @@
#define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
-/* allocation is serialized by namespace_sem */
+/*
+ * allocation is serialized by namespace_sem, but we need the spinlock to
+ * serialize with freeing.
+ */
static int mnt_alloc_id(struct vfsmount *mnt)
{
int res;
retry:
ida_pre_get(&mnt_id_ida, GFP_KERNEL);
- spin_lock(&vfsmount_lock);
+ spin_lock(&mnt_id_lock);
res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
if (!res)
mnt_id_start = mnt->mnt_id + 1;
- spin_unlock(&vfsmount_lock);
+ spin_unlock(&mnt_id_lock);
if (res == -EAGAIN)
goto retry;
@@ -86,11 +99,11 @@
static void mnt_free_id(struct vfsmount *mnt)
{
int id = mnt->mnt_id;
- spin_lock(&vfsmount_lock);
+ spin_lock(&mnt_id_lock);
ida_remove(&mnt_id_ida, id);
if (mnt_id_start > id)
mnt_id_start = id;
- spin_unlock(&vfsmount_lock);
+ spin_unlock(&mnt_id_lock);
}
/*
@@ -348,7 +361,7 @@
{
int ret = 0;
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
mnt->mnt_flags |= MNT_WRITE_HOLD;
/*
* After storing MNT_WRITE_HOLD, we'll read the counters. This store
@@ -382,15 +395,15 @@
*/
smp_wmb();
mnt->mnt_flags &= ~MNT_WRITE_HOLD;
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
return ret;
}
static void __mnt_unmake_readonly(struct vfsmount *mnt)
{
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
mnt->mnt_flags &= ~MNT_READONLY;
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
}
void simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
@@ -414,6 +427,7 @@
/*
* find the first or last mount at @dentry on vfsmount @mnt depending on
* @dir. If @dir is set return the first mount else return the last mount.
+ * vfsmount_lock must be held for read or write.
*/
struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
int dir)
@@ -443,10 +457,11 @@
struct vfsmount *lookup_mnt(struct path *path)
{
struct vfsmount *child_mnt;
- spin_lock(&vfsmount_lock);
+
+ br_read_lock(vfsmount_lock);
if ((child_mnt = __lookup_mnt(path->mnt, path->dentry, 1)))
mntget(child_mnt);
- spin_unlock(&vfsmount_lock);
+ br_read_unlock(vfsmount_lock);
return child_mnt;
}
@@ -455,6 +470,9 @@
return mnt->mnt_ns == current->nsproxy->mnt_ns;
}
+/*
+ * vfsmount lock must be held for write
+ */
static void touch_mnt_namespace(struct mnt_namespace *ns)
{
if (ns) {
@@ -463,6 +481,9 @@
}
}
+/*
+ * vfsmount lock must be held for write
+ */
static void __touch_mnt_namespace(struct mnt_namespace *ns)
{
if (ns && ns->event != event) {
@@ -471,6 +492,9 @@
}
}
+/*
+ * vfsmount lock must be held for write
+ */
static void detach_mnt(struct vfsmount *mnt, struct path *old_path)
{
old_path->dentry = mnt->mnt_mountpoint;
@@ -482,6 +506,9 @@
old_path->dentry->d_mounted--;
}
+/*
+ * vfsmount lock must be held for write
+ */
void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
struct vfsmount *child_mnt)
{
@@ -490,6 +517,9 @@
dentry->d_mounted++;
}
+/*
+ * vfsmount lock must be held for write
+ */
static void attach_mnt(struct vfsmount *mnt, struct path *path)
{
mnt_set_mountpoint(path->mnt, path->dentry, mnt);
@@ -499,7 +529,7 @@
}
/*
- * the caller must hold vfsmount_lock
+ * vfsmount lock must be held for write
*/
static void commit_tree(struct vfsmount *mnt)
{
@@ -623,39 +653,43 @@
void mntput_no_expire(struct vfsmount *mnt)
{
repeat:
- if (atomic_dec_and_lock(&mnt->mnt_count, &vfsmount_lock)) {
- if (likely(!mnt->mnt_pinned)) {
- spin_unlock(&vfsmount_lock);
- __mntput(mnt);
- return;
- }
- atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count);
- mnt->mnt_pinned = 0;
- spin_unlock(&vfsmount_lock);
- acct_auto_close_mnt(mnt);
- goto repeat;
+ if (atomic_add_unless(&mnt->mnt_count, -1, 1))
+ return;
+ br_write_lock(vfsmount_lock);
+ if (!atomic_dec_and_test(&mnt->mnt_count)) {
+ br_write_unlock(vfsmount_lock);
+ return;
}
+ if (likely(!mnt->mnt_pinned)) {
+ br_write_unlock(vfsmount_lock);
+ __mntput(mnt);
+ return;
+ }
+ atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count);
+ mnt->mnt_pinned = 0;
+ br_write_unlock(vfsmount_lock);
+ acct_auto_close_mnt(mnt);
+ goto repeat;
}
-
EXPORT_SYMBOL(mntput_no_expire);
void mnt_pin(struct vfsmount *mnt)
{
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
mnt->mnt_pinned++;
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
}
EXPORT_SYMBOL(mnt_pin);
void mnt_unpin(struct vfsmount *mnt)
{
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
if (mnt->mnt_pinned) {
atomic_inc(&mnt->mnt_count);
mnt->mnt_pinned--;
}
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
}
EXPORT_SYMBOL(mnt_unpin);
@@ -746,12 +780,12 @@
struct mnt_namespace *ns = p->ns;
int res = 0;
- spin_lock(&vfsmount_lock);
+ br_read_lock(vfsmount_lock);
if (p->event != ns->event) {
p->event = ns->event;
res = 1;
}
- spin_unlock(&vfsmount_lock);
+ br_read_unlock(vfsmount_lock);
return res;
}
@@ -952,12 +986,12 @@
int minimum_refs = 0;
struct vfsmount *p;
- spin_lock(&vfsmount_lock);
+ br_read_lock(vfsmount_lock);
for (p = mnt; p; p = next_mnt(p, mnt)) {
actual_refs += atomic_read(&p->mnt_count);
minimum_refs += 2;
}
- spin_unlock(&vfsmount_lock);
+ br_read_unlock(vfsmount_lock);
if (actual_refs > minimum_refs)
return 0;
@@ -984,10 +1018,10 @@
{
int ret = 1;
down_read(&namespace_sem);
- spin_lock(&vfsmount_lock);
+ br_read_lock(vfsmount_lock);
if (propagate_mount_busy(mnt, 2))
ret = 0;
- spin_unlock(&vfsmount_lock);
+ br_read_unlock(vfsmount_lock);
up_read(&namespace_sem);
return ret;
}
@@ -1003,13 +1037,14 @@
if (mnt->mnt_parent != mnt) {
struct dentry *dentry;
struct vfsmount *m;
- spin_lock(&vfsmount_lock);
+
+ br_write_lock(vfsmount_lock);
dentry = mnt->mnt_mountpoint;
m = mnt->mnt_parent;
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
m->mnt_ghosts--;
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
dput(dentry);
mntput(m);
}
@@ -1017,6 +1052,10 @@
}
}
+/*
+ * vfsmount lock must be held for write
+ * namespace_sem must be held for write
+ */
void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
{
struct vfsmount *p;
@@ -1107,7 +1146,7 @@
}
down_write(&namespace_sem);
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
event++;
if (!(flags & MNT_DETACH))
@@ -1119,7 +1158,7 @@
umount_tree(mnt, 1, &umount_list);
retval = 0;
}
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
release_mounts(&umount_list);
return retval;
@@ -1231,19 +1270,19 @@
q = clone_mnt(p, p->mnt_root, flag);
if (!q)
goto Enomem;
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
list_add_tail(&q->mnt_list, &res->mnt_list);
attach_mnt(q, &path);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
}
}
return res;
Enomem:
if (res) {
LIST_HEAD(umount_list);
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
umount_tree(res, 0, &umount_list);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
release_mounts(&umount_list);
}
return NULL;
@@ -1262,9 +1301,9 @@
{
LIST_HEAD(umount_list);
down_write(&namespace_sem);
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
umount_tree(mnt, 0, &umount_list);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
release_mounts(&umount_list);
}
@@ -1392,7 +1431,7 @@
if (err)
goto out_cleanup_ids;
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
if (IS_MNT_SHARED(dest_mnt)) {
for (p = source_mnt; p; p = next_mnt(p, source_mnt))
@@ -1411,7 +1450,8 @@
list_del_init(&child->mnt_hash);
commit_tree(child);
}
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
+
return 0;
out_cleanup_ids:
@@ -1466,10 +1506,10 @@
goto out_unlock;
}
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
change_mnt_propagation(m, type);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
out_unlock:
up_write(&namespace_sem);
@@ -1513,9 +1553,10 @@
err = graft_tree(mnt, path);
if (err) {
LIST_HEAD(umount_list);
- spin_lock(&vfsmount_lock);
+
+ br_write_lock(vfsmount_lock);
umount_tree(mnt, 0, &umount_list);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
release_mounts(&umount_list);
}
@@ -1568,16 +1609,16 @@
else
err = do_remount_sb(sb, flags, data, 0);
if (!err) {
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
mnt_flags |= path->mnt->mnt_flags & MNT_PROPAGATION_MASK;
path->mnt->mnt_flags = mnt_flags;
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
}
up_write(&sb->s_umount);
if (!err) {
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
touch_mnt_namespace(path->mnt->mnt_ns);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
}
return err;
}
@@ -1754,7 +1795,7 @@
return;
down_write(&namespace_sem);
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
/* extract from the expiration list every vfsmount that matches the
* following criteria:
@@ -1773,7 +1814,7 @@
touch_mnt_namespace(mnt->mnt_ns);
umount_tree(mnt, 1, &umounts);
}
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
release_mounts(&umounts);
@@ -1830,6 +1871,8 @@
/*
* 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
*/
static void shrink_submounts(struct vfsmount *mnt, struct list_head *umounts)
{
@@ -2048,9 +2091,9 @@
kfree(new_ns);
return ERR_PTR(-ENOMEM);
}
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
/*
* Second pass: switch the tsk->fs->* elements and mark new vfsmounts
@@ -2244,7 +2287,7 @@
goto out2; /* not attached */
/* make sure we can reach put_old from new_root */
tmp = old.mnt;
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
if (tmp != new.mnt) {
for (;;) {
if (tmp->mnt_parent == tmp)
@@ -2264,7 +2307,7 @@
/* mount new_root on / */
attach_mnt(new.mnt, &root_parent);
touch_mnt_namespace(current->nsproxy->mnt_ns);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
chroot_fs_refs(&root, &new);
error = 0;
path_put(&root_parent);
@@ -2279,7 +2322,7 @@
out0:
return error;
out3:
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
goto out2;
}
@@ -2326,6 +2369,8 @@
for (u = 0; u < HASH_SIZE; u++)
INIT_LIST_HEAD(&mount_hashtable[u]);
+ br_lock_init(vfsmount_lock);
+
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
@@ -2344,9 +2389,9 @@
if (!atomic_dec_and_test(&ns->count))
return;
down_write(&namespace_sem);
- spin_lock(&vfsmount_lock);
+ br_write_lock(vfsmount_lock);
umount_tree(ns->root, 0, &umount_list);
- spin_unlock(&vfsmount_lock);
+ br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
release_mounts(&umount_list);
kfree(ns);
