inotify: seperate new watch creation updating existing watches

There is nothing known wrong with the inotify watch addition/modification
but this patch seperates the two code paths to make them each easy to
verify as correct.

Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 103 insertions, 69 deletions

diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index dc32ed8323ba..d8f73c253073 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -431,80 +431,29 @@ static void inotify_free_mark(struct fsnotify_mark_entry *entry)
         kmem_cache_free(inotify_inode_mark_cachep, ientry);
 }
 
-static int inotify_update_watch(struct fsnotify_group *group, struct inode *inode, u32 arg)
+static int inotify_update_existing_watch(struct fsnotify_group *group,
+                                         struct inode *inode,
+                                         u32 arg)
 {
-        struct fsnotify_mark_entry *entry = NULL;
+        struct fsnotify_mark_entry *entry;
         struct inotify_inode_mark_entry *ientry;
-        struct inotify_inode_mark_entry *tmp_ientry;
-        int ret = 0;
-        int add = (arg & IN_MASK_ADD);
-        __u32 mask;
         __u32 old_mask, new_mask;
+        __u32 mask;
+        int add = (arg & IN_MASK_ADD);
+        int ret;
 
         /* don't allow invalid bits: we don't want flags set */
         mask = inotify_arg_to_mask(arg);
         if (unlikely(!mask))
                 return -EINVAL;
 
-        tmp_ientry = kmem_cache_alloc(inotify_inode_mark_cachep, GFP_KERNEL);
-        if (unlikely(!tmp_ientry))
-                return -ENOMEM;
-        /* we set the mask at the end after attaching it */
-        fsnotify_init_mark(&tmp_ientry->fsn_entry, inotify_free_mark);
-        tmp_ientry->wd = -1;
-
-find_entry:
         spin_lock(&inode->i_lock);
         entry = fsnotify_find_mark_entry(group, inode);
         spin_unlock(&inode->i_lock);
-        if (entry) {
-                ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry);
-        } else {
-                ret = -ENOSPC;
-                if (atomic_read(&group->inotify_data.user->inotify_watches) >= inotify_max_user_watches)
-                        goto out_err;
-retry:
-                ret = -ENOMEM;
-                if (unlikely(!idr_pre_get(&group->inotify_data.idr, GFP_KERNEL)))
-                        goto out_err;
-
-                spin_lock(&group->inotify_data.idr_lock);
-                ret = idr_get_new_above(&group->inotify_data.idr, &tmp_ientry->fsn_entry,
-                                        group->inotify_data.last_wd,
-                                        &tmp_ientry->wd);
-                spin_unlock(&group->inotify_data.idr_lock);
-                if (ret) {
-                        if (ret == -EAGAIN)
-                                goto retry;
-                        goto out_err;
-                }
+        if (!entry)
+                return -ENOENT;
 
-                ret = fsnotify_add_mark(&tmp_ientry->fsn_entry, group, inode);
-                if (ret) {
-                        inotify_remove_from_idr(group, tmp_ientry);
-                        if (ret == -EEXIST)
-                                goto find_entry;
-                        goto out_err;
-                }
-
-                /* tmp_ientry has been added to the inode, so we are all set up.
-                 * now we just need to make sure tmp_ientry doesn't get freed and
-                 * we need to set up entry and ientry so the generic code can
-                 * do its thing. */
-                ientry = tmp_ientry;
-                entry = &ientry->fsn_entry;
-                tmp_ientry = NULL;
-
-                atomic_inc(&group->inotify_data.user->inotify_watches);
-
-                /* update the idr hint */
-                group->inotify_data.last_wd = ientry->wd;
-
-                /* we put the mark on the idr, take a reference */
-                fsnotify_get_mark(entry);
-        }
-
-        ret = ientry->wd;
+        ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry);
 
         spin_lock(&entry->lock);
 
@@ -536,18 +485,103 @@ retry:
                         fsnotify_recalc_group_mask(group);
         }
 
-        /* this either matches fsnotify_find_mark_entry, or init_mark_entry
-         * depending on which path we took... */
+        /* return the wd */
+        ret = ientry->wd;
+
+        /* match the get from fsnotify_find_mark_entry() */
         fsnotify_put_mark(entry);
 
+        return ret;
+}
+
+static int inotify_new_watch(struct fsnotify_group *group,
+                             struct inode *inode,
+                             u32 arg)
+{
+        struct inotify_inode_mark_entry *tmp_ientry;
+        __u32 mask;
+        int ret;
+
+        /* don't allow invalid bits: we don't want flags set */
+        mask = inotify_arg_to_mask(arg);
+        if (unlikely(!mask))
+                return -EINVAL;
+
+        tmp_ientry = kmem_cache_alloc(inotify_inode_mark_cachep, GFP_KERNEL);
+        if (unlikely(!tmp_ientry))
+                return -ENOMEM;
+
+        fsnotify_init_mark(&tmp_ientry->fsn_entry, inotify_free_mark);
+        tmp_ientry->fsn_entry.mask = mask;
+        tmp_ientry->wd = -1;
+
+        ret = -ENOSPC;
+        if (atomic_read(&group->inotify_data.user->inotify_watches) >= inotify_max_user_watches)
+                goto out_err;
+retry:
+        ret = -ENOMEM;
+        if (unlikely(!idr_pre_get(&group->inotify_data.idr, GFP_KERNEL)))
+                goto out_err;
+
+        spin_lock(&group->inotify_data.idr_lock);
+        ret = idr_get_new_above(&group->inotify_data.idr, &tmp_ientry->fsn_entry,
+                                group->inotify_data.last_wd,
+                                &tmp_ientry->wd);
+        spin_unlock(&group->inotify_data.idr_lock);
+        if (ret) {
+                /* idr was out of memory allocate and try again */
+                if (ret == -EAGAIN)
+                        goto retry;
+                goto out_err;
+        }
+
+        /* we are on the idr, now get on the inode */
+        ret = fsnotify_add_mark(&tmp_ientry->fsn_entry, group, inode);
+        if (ret) {
+                /* we failed to get on the inode, get off the idr */
+                inotify_remove_from_idr(group, tmp_ientry);
+                goto out_err;
+        }
+
+        /* we put the mark on the idr, take a reference */
+        fsnotify_get_mark(&tmp_ientry->fsn_entry);
+
+        /* update the idr hint, who cares about races, it's just a hint */
+        group->inotify_data.last_wd = tmp_ientry->wd;
+
+        /* increment the number of watches the user has */
+        atomic_inc(&group->inotify_data.user->inotify_watches);
+
+        /* return the watch descriptor for this new entry */
+        ret = tmp_ientry->wd;
+
+        /* match the ref from fsnotify_init_markentry() */
+        fsnotify_put_mark(&tmp_ientry->fsn_entry);
+
 out_err:
-        /* could be an error, could be that we found an existing mark */
-        if (tmp_ientry) {
-                /* on the idr but didn't make it on the inode */
-                if (tmp_ientry->wd != -1)
-                        inotify_remove_from_idr(group, tmp_ientry);
+        if (ret < 0)
                 kmem_cache_free(inotify_inode_mark_cachep, tmp_ientry);
-        }
+
+        return ret;
+}
+
+static int inotify_update_watch(struct fsnotify_group *group, struct inode *inode, u32 arg)
+{
+        int ret = 0;
+
+retry:
+        /* try to update and existing watch with the new arg */
+        ret = inotify_update_existing_watch(group, inode, arg);
+        /* no mark present, try to add a new one */
+        if (ret == -ENOENT)
+                ret = inotify_new_watch(group, inode, arg);
+        /*
+         * inotify_new_watch could race with another thread which did an
+         * inotify_new_watch between the update_existing and the add watch
+         * here, go back and try to update an existing mark again.
+         */
+        if (ret == -EEXIST)
+                goto retry;
 
         return ret;
 }