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sanitize vfsmount refcounting changes

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Instead of splitting refcount between (per-cpu) mnt_count
and (SMP-only) mnt_longrefs, make all references contribute
to mnt_count again and keep track of how many are longterm
ones.

Accounting rules for longterm count:
	* 1 for each fs_struct.root.mnt
	* 1 for each fs_struct.pwd.mnt
	* 1 for having non-NULL ->mnt_ns
	* decrement to 0 happens only under vfsmount lock exclusive

That allows nice common case for mntput() - since we can't drop the
final reference until after mnt_longterm has reached 0 due to the rules
above, mntput() can grab vfsmount lock shared and check mnt_longterm.
If it turns out to be non-zero (which is the common case), we know
that this is not the final mntput() and can just blindly decrement
percpu mnt_count.  Otherwise we grab vfsmount lock exclusive and
do usual decrement-and-check of percpu mnt_count.

For fs_struct.c we have mnt_make_longterm() and mnt_make_shortterm();
namespace.c uses the latter in places where we don't already hold
vfsmount lock exclusive and opencodes a few remaining spots where
we need to manipulate mnt_longterm.

Note that we mostly revert the code outside of fs/namespace.c back
to what we used to have; in particular, normal code doesn't need
to care about two kinds of references, etc.  And we get to keep
the optimization Nick's variant had bought us...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2011-01-14 22:30:21 -05:00
parent 7b8a53fd81
commit f03c65993b
10 changed files with 75 additions and 117 deletions
Download Patch File Download Diff File Expand all files Collapse all files

116
fs/namespace.c
View File

@ -183,7 +183,7 @@ static inline void mnt_dec_count(struct vfsmount *mnt)
unsigned int mnt_get_count(struct vfsmount *mnt)
{
#ifdef CONFIG_SMP
unsigned int count = atomic_read(&mnt->mnt_longrefs);
unsigned int count = 0;
int cpu;
for_each_possible_cpu(cpu) {
@ -217,7 +217,7 @@ struct vfsmount *alloc_vfsmnt(const char *name)
if (!mnt->mnt_pcp)
goto out_free_devname;
atomic_set(&mnt->mnt_longrefs, 1);
this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
#else
mnt->mnt_count = 1;
mnt->mnt_writers = 0;
@ -624,8 +624,11 @@ static void commit_tree(struct vfsmount *mnt)
BUG_ON(parent == mnt);
list_add_tail(&head, &mnt->mnt_list);
list_for_each_entry(m, &head, mnt_list)
list_for_each_entry(m, &head, mnt_list) {
m->mnt_ns = n;
atomic_inc(&m->mnt_longterm);
}
list_splice(&head, n->list.prev);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
@ -734,51 +737,30 @@ static inline void mntfree(struct vfsmount *mnt)
deactivate_super(sb);
}
#ifdef CONFIG_SMP
static inline void __mntput(struct vfsmount *mnt, int longrefs)
static void mntput_no_expire(struct vfsmount *mnt)
{
if (!longrefs) {
put_again:
br_read_lock(vfsmount_lock);
if (likely(atomic_read(&mnt->mnt_longrefs))) {
mnt_dec_count(mnt);
br_read_unlock(vfsmount_lock);
return;
}
#ifdef CONFIG_SMP
br_read_lock(vfsmount_lock);
if (likely(atomic_read(&mnt->mnt_longterm))) {
mnt_dec_count(mnt);
br_read_unlock(vfsmount_lock);
} else {
BUG_ON(!atomic_read(&mnt->mnt_longrefs));
if (atomic_add_unless(&mnt->mnt_longrefs, -1, 1))
return;
return;
}
br_read_unlock(vfsmount_lock);
br_write_lock(vfsmount_lock);
if (!longrefs)
mnt_dec_count(mnt);
else
atomic_dec(&mnt->mnt_longrefs);
mnt_dec_count(mnt);
if (mnt_get_count(mnt)) {
br_write_unlock(vfsmount_lock);
return;
}
if (unlikely(mnt->mnt_pinned)) {
mnt_add_count(mnt, mnt->mnt_pinned + 1);
mnt->mnt_pinned = 0;
br_write_unlock(vfsmount_lock);
acct_auto_close_mnt(mnt);
goto put_again;
}
br_write_unlock(vfsmount_lock);
mntfree(mnt);
}
#else
static inline void __mntput(struct vfsmount *mnt, int longrefs)
{
put_again:
mnt_dec_count(mnt);
if (likely(mnt_get_count(mnt)))
return;
br_write_lock(vfsmount_lock);
#endif
if (unlikely(mnt->mnt_pinned)) {
mnt_add_count(mnt, mnt->mnt_pinned + 1);
mnt->mnt_pinned = 0;
@ -789,12 +771,6 @@ put_again:
br_write_unlock(vfsmount_lock);
mntfree(mnt);
}
#endif
static void mntput_no_expire(struct vfsmount *mnt)
{
__mntput(mnt, 0);
}
void mntput(struct vfsmount *mnt)
{
@ -802,7 +778,7 @@ void mntput(struct vfsmount *mnt)
/* avoid cacheline pingpong, hope gcc doesn't get "smart" */
if (unlikely(mnt->mnt_expiry_mark))
mnt->mnt_expiry_mark = 0;
__mntput(mnt, 0);
mntput_no_expire(mnt);
}
}
EXPORT_SYMBOL(mntput);
@ -815,33 +791,6 @@ struct vfsmount *mntget(struct vfsmount *mnt)
}
EXPORT_SYMBOL(mntget);
void mntput_long(struct vfsmount *mnt)
{
#ifdef CONFIG_SMP
if (mnt) {
/* avoid cacheline pingpong, hope gcc doesn't get "smart" */
if (unlikely(mnt->mnt_expiry_mark))
mnt->mnt_expiry_mark = 0;
__mntput(mnt, 1);
}
#else
mntput(mnt);
#endif
}
EXPORT_SYMBOL(mntput_long);
struct vfsmount *mntget_long(struct vfsmount *mnt)
{
#ifdef CONFIG_SMP
if (mnt)
atomic_inc(&mnt->mnt_longrefs);
return mnt;
#else
return mntget(mnt);
#endif
}
EXPORT_SYMBOL(mntget_long);
void mnt_pin(struct vfsmount *mnt)
{
br_write_lock(vfsmount_lock);
@ -1216,7 +1165,7 @@ void release_mounts(struct list_head *head)
dput(dentry);
mntput(m);
}
mntput_long(mnt);
mntput(mnt);
}
}
@ -1240,6 +1189,7 @@ void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
list_del_init(&p->mnt_list);
__touch_mnt_namespace(p->mnt_ns);
p->mnt_ns = NULL;
atomic_dec(&p->mnt_longterm);
list_del_init(&p->mnt_child);
if (p->mnt_parent != p) {
p->mnt_parent->mnt_ghosts++;
@ -1969,7 +1919,7 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags)
unlock:
up_write(&namespace_sem);
mntput_long(newmnt);
mntput(newmnt);
return err;
}
@ -2291,6 +2241,20 @@ static struct mnt_namespace *alloc_mnt_ns(void)
return new_ns;
}
void mnt_make_longterm(struct vfsmount *mnt)
{
atomic_inc(&mnt->mnt_longterm);
}
void mnt_make_shortterm(struct vfsmount *mnt)
{
if (atomic_add_unless(&mnt->mnt_longterm, -1, 1))
return;
br_write_lock(vfsmount_lock);
atomic_dec(&mnt->mnt_longterm);
br_write_unlock(vfsmount_lock);
}
/*
* Allocate a new namespace structure and populate it with contents
* copied from the namespace of the passed in task structure.
@ -2328,14 +2292,19 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
q = new_ns->root;
while (p) {
q->mnt_ns = new_ns;
atomic_inc(&q->mnt_longterm);
if (fs) {
if (p == fs->root.mnt) {
fs->root.mnt = mntget(q);
atomic_inc(&q->mnt_longterm);
mnt_make_shortterm(p);
rootmnt = p;
fs->root.mnt = mntget_long(q);
}
if (p == fs->pwd.mnt) {
fs->pwd.mnt = mntget(q);
atomic_inc(&q->mnt_longterm);
mnt_make_shortterm(p);
pwdmnt = p;
fs->pwd.mnt = mntget_long(q);
}
}
p = next_mnt(p, mnt_ns->root);
@ -2344,9 +2313,9 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
up_write(&namespace_sem);
if (rootmnt)
mntput_long(rootmnt);
mntput(rootmnt);
if (pwdmnt)
mntput_long(pwdmnt);
mntput(pwdmnt);
return new_ns;
}
@ -2379,6 +2348,7 @@ struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt)
new_ns = alloc_mnt_ns();
if (!IS_ERR(new_ns)) {
mnt->mnt_ns = new_ns;
atomic_inc(&mnt->mnt_longterm);
new_ns->root = mnt;
list_add(&new_ns->list, &new_ns->root->mnt_list);
}