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>

diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index dc32ed8..d8f73c2 100644 (file)
--- 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;
 }