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fsnotify: Lock object list with connector lock
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So far list of marks attached to an object (inode / vfsmount) was
protected by i_lock or mnt_root->d_lock. This dictates that the list
must be empty before the object can be destroyed although the list is
now anchored in the fsnotify_mark_connector structure. Protect the list
by a spinlock in the fsnotify_mark_connector structure to decouple
lifetime of a list of marks from a lifetime of the object. This also
simplifies the code quite a bit since we don't have to differentiate
between inode and vfsmount lists in quite a few places anymore.

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
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Jan Kara committed Apr 10, 2017
1 parent 2629718 commit 04662ca
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Showing 2 changed files with 34 additions and 59 deletions.
90 changes: 32 additions & 58 deletions fs/notify/mark.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@
*
* group->mark_mutex
* mark->lock
* inode->i_lock
* mark->connector->lock
*
* group->mark_mutex protects the marks_list anchored inside a given group and
* each mark is hooked via the g_list. It also protects the groups private
Expand All @@ -44,10 +44,12 @@
* is assigned to as well as the access to a reference of the inode/vfsmount
* that is being watched by the mark.
*
* inode->i_lock protects the i_fsnotify_marks list anchored inside a
* given inode and each mark is hooked via the i_list. (and sorta the
* free_i_list)
* mark->connector->lock protects the list of marks anchored inside an
* inode / vfsmount and each mark is hooked via the i_list.
*
* A list of notification marks relating to inode / mnt is contained in
* fsnotify_mark_connector. That structure is alive as long as there are any
* marks in the list and is also protected by fsnotify_mark_srcu.
*
* LIFETIME:
* Inode marks survive between when they are added to an inode and when their
Expand Down Expand Up @@ -110,8 +112,10 @@ static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
u32 new_mask = 0;
struct fsnotify_mark *mark;

assert_spin_locked(&conn->lock);
hlist_for_each_entry(mark, &conn->list, obj_list)
new_mask |= mark->mask;

if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
conn->inode->i_fsnotify_mask = new_mask;
else if (conn->flags & FSNOTIFY_OBJ_TYPE_VFSMOUNT)
Expand All @@ -128,39 +132,28 @@ void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
if (!conn)
return;

if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
spin_lock(&conn->inode->i_lock);
else
spin_lock(&conn->mnt->mnt_root->d_lock);
spin_lock(&conn->lock);
__fsnotify_recalc_mask(conn);
if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE) {
spin_unlock(&conn->inode->i_lock);
spin_unlock(&conn->lock);
if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
__fsnotify_update_child_dentry_flags(conn->inode);
} else {
spin_unlock(&conn->mnt->mnt_root->d_lock);
}
}

static struct inode *fsnotify_detach_from_object(struct fsnotify_mark *mark)
{
struct fsnotify_mark_connector *conn;
struct inode *inode = NULL;
spinlock_t *lock;

conn = mark->connector;
if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
lock = &conn->inode->i_lock;
else
lock = &conn->mnt->mnt_root->d_lock;
spin_lock(lock);
spin_lock(&conn->lock);
hlist_del_init_rcu(&mark->obj_list);
if (hlist_empty(&conn->list)) {
if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
inode = conn->inode;
}
__fsnotify_recalc_mask(conn);
mark->connector = NULL;
spin_unlock(lock);
spin_unlock(&conn->lock);

return inode;
}
Expand Down Expand Up @@ -326,7 +319,6 @@ int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)

static int fsnotify_attach_connector_to_object(
struct fsnotify_mark_connector **connp,
spinlock_t *lock,
struct inode *inode,
struct vfsmount *mnt)
{
Expand All @@ -335,6 +327,7 @@ static int fsnotify_attach_connector_to_object(
conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
if (!conn)
return -ENOMEM;
spin_lock_init(&conn->lock);
INIT_HLIST_HEAD(&conn->list);
if (inode) {
conn->flags = FSNOTIFY_OBJ_TYPE_INODE;
Expand All @@ -344,16 +337,13 @@ static int fsnotify_attach_connector_to_object(
conn->mnt = mnt;
}
/*
* Make sure 'conn' initialization is visible. Matches
* lockless_dereference() in fsnotify().
* cmpxchg() provides the barrier so that readers of *connp can see
* only initialized structure
*/
smp_wmb();
spin_lock(lock);
if (!*connp)
*connp = conn;
else
if (cmpxchg(connp, NULL, conn)) {
/* Someone else created list structure for us */
kmem_cache_free(fsnotify_mark_connector_cachep, conn);
spin_unlock(lock);
}

return 0;
}
Expand All @@ -371,35 +361,30 @@ static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
struct fsnotify_mark *lmark, *last = NULL;
struct fsnotify_mark_connector *conn;
struct fsnotify_mark_connector **connp;
spinlock_t *lock;
int cmp;
int err = 0;

if (WARN_ON(!inode && !mnt))
return -EINVAL;
if (inode) {
if (inode)
connp = &inode->i_fsnotify_marks;
lock = &inode->i_lock;
} else {
else
connp = &real_mount(mnt)->mnt_fsnotify_marks;
lock = &mnt->mnt_root->d_lock;
}

if (!*connp) {
err = fsnotify_attach_connector_to_object(connp, lock,
inode, mnt);
err = fsnotify_attach_connector_to_object(connp, inode, mnt);
if (err)
return err;
}
spin_lock(&mark->lock);
spin_lock(lock);
conn = *connp;
spin_lock(&conn->lock);

/* is mark the first mark? */
if (hlist_empty(&conn->list)) {
hlist_add_head_rcu(&mark->obj_list, &conn->list);
if (inode)
__iget(inode);
igrab(inode);
goto added;
}

Expand All @@ -425,7 +410,7 @@ static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
added:
mark->connector = conn;
out_err:
spin_unlock(lock);
spin_unlock(&conn->lock);
spin_unlock(&mark->lock);
return err;
}
Expand All @@ -449,7 +434,7 @@ int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
* LOCKING ORDER!!!!
* group->mark_mutex
* mark->lock
* inode->i_lock
* mark->connector->lock
*/
spin_lock(&mark->lock);
mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
Expand Down Expand Up @@ -505,24 +490,19 @@ struct fsnotify_mark *fsnotify_find_mark(struct fsnotify_mark_connector *conn,
struct fsnotify_group *group)
{
struct fsnotify_mark *mark;
spinlock_t *lock;

if (!conn)
return NULL;

if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
lock = &conn->inode->i_lock;
else
lock = &conn->mnt->mnt_root->d_lock;
spin_lock(lock);
spin_lock(&conn->lock);
hlist_for_each_entry(mark, &conn->list, obj_list) {
if (mark->group == group) {
fsnotify_get_mark(mark);
spin_unlock(lock);
spin_unlock(&conn->lock);
return mark;
}
}
spin_unlock(lock);
spin_unlock(&conn->lock);
return NULL;
}

Expand Down Expand Up @@ -595,16 +575,10 @@ void fsnotify_detach_group_marks(struct fsnotify_group *group)
void fsnotify_destroy_marks(struct fsnotify_mark_connector *conn)
{
struct fsnotify_mark *mark;
spinlock_t *lock;

if (!conn)
return;

if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
lock = &conn->inode->i_lock;
else
lock = &conn->mnt->mnt_root->d_lock;

while (1) {
/*
* We have to be careful since we can race with e.g.
Expand All @@ -613,15 +587,15 @@ void fsnotify_destroy_marks(struct fsnotify_mark_connector *conn)
* we are holding mark reference so mark cannot be freed and
* calling fsnotify_destroy_mark() more than once is fine.
*/
spin_lock(lock);
spin_lock(&conn->lock);
if (hlist_empty(&conn->list)) {
spin_unlock(lock);
spin_unlock(&conn->lock);
break;
}
mark = hlist_entry(conn->list.first, struct fsnotify_mark,
obj_list);
fsnotify_get_mark(mark);
spin_unlock(lock);
spin_unlock(&conn->lock);
fsnotify_destroy_mark(mark, mark->group);
fsnotify_put_mark(mark);
}
Expand Down
3 changes: 2 additions & 1 deletion include/linux/fsnotify_backend.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -201,6 +201,7 @@ struct fsnotify_group {
* inode / vfsmount gets freed.
*/
struct fsnotify_mark_connector {
spinlock_t lock;
#define FSNOTIFY_OBJ_TYPE_INODE 0x01
#define FSNOTIFY_OBJ_TYPE_VFSMOUNT 0x02
unsigned int flags; /* Type of object [lock] */
Expand Down Expand Up @@ -240,7 +241,7 @@ struct fsnotify_mark {
struct list_head g_list;
/* Protects inode / mnt pointers, flags, masks */
spinlock_t lock;
/* List of marks for inode / vfsmount [obj_lock] */
/* List of marks for inode / vfsmount [connector->lock] */
struct hlist_node obj_list;
/* Head of list of marks for an object [mark->lock, group->mark_mutex] */
struct fsnotify_mark_connector *connector;
Expand Down

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