Re: [PATCH 4/4] fsnotify: clean up fsnotify()

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On Fri, Oct 20, 2017 at 2:48 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> On Thu, Oct 19, 2017 at 4:58 PM, Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
>> Use helpers to get first and next marks from connector.
>>
>> Also get rid of inode_node/vfsmount_node local variables, which just refers
>> to the same objects as iter_info.  There was an srcu_dereference() for
>> foo_node, but that's completely superfluous since we've already done it
>> when obtaining foo_node.
>>
>> Also get rid of inode_group/vfsmount_group local variables; checking
>> against non-NULL for these is the same as checking against non-NULL
>> inode_mark/vfsmount_mark.
>>
>
> Nice Cleanup!
>
>> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
>> ---
>>  fs/notify/fsnotify.c | 107 +++++++++++++++++++++++----------------------------
>>  1 file changed, 48 insertions(+), 59 deletions(-)
>>
>> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
>> index 0ab6a7179e4d..7490edd74883 100644
>> --- a/fs/notify/fsnotify.c
>> +++ b/fs/notify/fsnotify.c
>> @@ -243,6 +243,28 @@ static int send_to_group(struct inode *to_tell,
>>                                         file_name, cookie, iter_info);
>>  }
>>
>> +static struct fsnotify_mark *fsnotify_first_mark(struct fsnotify_mark_connector **connp)
>> +{
>> +       struct fsnotify_mark_connector *conn;
>> +       struct hlist_node *node = NULL;
>> +
>> +       conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
>> +       if (conn)
>> +               node = srcu_dereference(conn->list.first, &fsnotify_mark_srcu);
>> +
>> +       return hlist_entry_safe(node, struct fsnotify_mark, obj_list);
>> +}
>> +
>> +static struct fsnotify_mark *fsnotify_next_mark(struct fsnotify_mark *mark)
>> +{
>> +       struct hlist_node *node = NULL;
>> +
>> +       if (mark)
>> +               node = srcu_dereference(mark->obj_list.next, &fsnotify_mark_srcu);
>> +
>> +       return hlist_entry_safe(node, struct fsnotify_mark, obj_list);
>> +}
>> +
>>  /*
>>   * This is the main call to fsnotify.  The VFS calls into hook specific functions
>>   * in linux/fsnotify.h.  Those functions then in turn call here.  Here will call
>> @@ -252,11 +274,7 @@ static int send_to_group(struct inode *to_tell,
>>  int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
>>              const unsigned char *file_name, u32 cookie)
>>  {
>> -       struct hlist_node *inode_node = NULL, *vfsmount_node = NULL;
>> -       struct fsnotify_mark *inode_mark = NULL, *vfsmount_mark = NULL;
>> -       struct fsnotify_group *inode_group, *vfsmount_group;
>> -       struct fsnotify_mark_connector *inode_conn, *vfsmount_conn;
>> -       struct fsnotify_iter_info iter_info;
>> +       struct fsnotify_iter_info iter_info = { NULL, NULL };
>
> There was a series of security patches converting those initializers to { }
> don't ask me why.

Okay.

>
>>         struct mount *mnt;
>>         int ret = 0;
>>         /* global tests shouldn't care about events on child only the specific event */
>> @@ -291,26 +309,13 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
>>
>>         if ((mask & FS_MODIFY) ||
>>             (test_mask & to_tell->i_fsnotify_mask)) {
>> -               inode_conn = srcu_dereference(to_tell->i_fsnotify_marks,
>> -                                             &fsnotify_mark_srcu);
>> -               if (inode_conn)
>> -                       inode_node = srcu_dereference(inode_conn->list.first,
>> -                                                     &fsnotify_mark_srcu);
>> +               iter_info.inode_mark = fsnotify_first_mark(&to_tell->i_fsnotify_marks);
>>         }
>>
>>         if (mnt && ((mask & FS_MODIFY) ||
>>                     (test_mask & mnt->mnt_fsnotify_mask))) {
>> -               inode_conn = srcu_dereference(to_tell->i_fsnotify_marks,
>> -                                             &fsnotify_mark_srcu);
>> -               if (inode_conn)
>> -                       inode_node = srcu_dereference(inode_conn->list.first,
>> -                                                     &fsnotify_mark_srcu);
>> -               vfsmount_conn = srcu_dereference(mnt->mnt_fsnotify_marks,
>> -                                                &fsnotify_mark_srcu);
>> -               if (vfsmount_conn)
>> -                       vfsmount_node = srcu_dereference(
>> -                                               vfsmount_conn->list.first,
>> -                                               &fsnotify_mark_srcu);
>> +               iter_info.inode_mark = fsnotify_first_mark(&to_tell->i_fsnotify_marks);
>> +               iter_info.vfsmount_mark = fsnotify_first_mark(&mnt->mnt_fsnotify_marks);
>>         }
>>
>>         /*
>> @@ -318,41 +323,28 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
>>          * ignore masks are properly reflected for mount mark notifications.
>>          * That's why this traversal is so complicated...
>>          */
>> -       while (inode_node || vfsmount_node) {
>> -               inode_group = NULL;
>> -               inode_mark = NULL;
>> -               vfsmount_group = NULL;
>> -               vfsmount_mark = NULL;
>> -
>> -               if (inode_node) {
>> -                       inode_mark = hlist_entry(srcu_dereference(inode_node, &fsnotify_mark_srcu),
>> -                                                struct fsnotify_mark, obj_list);
>> -                       inode_group = inode_mark->group;
>> -                       if (!(inode_mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED))
>> -                               goto skip_inode;
>> -               }
>> +       while (iter_info.inode_mark || iter_info.vfsmount_mark) {
>> +               struct fsnotify_mark *inode_mark = iter_info.inode_mark;
>> +               struct fsnotify_mark *vfsmount_mark = iter_info.vfsmount_mark;
>>
>> -               if (vfsmount_node) {
>> -                       vfsmount_mark = hlist_entry(srcu_dereference(vfsmount_node, &fsnotify_mark_srcu),
>> -                                                   struct fsnotify_mark, obj_list);
>> -                       vfsmount_group = vfsmount_mark->group;
>> -                       if (!(vfsmount_mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED))
>> -                               goto skip_vfsmount;
>> +               if (inode_mark &&
>> +                   !(inode_mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
>> +                       vfsmount_mark = NULL;
>> +                       goto skip;
>> +               }
>> +               if (vfsmount_mark &&
>> +                   !(vfsmount_mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
>> +                       inode_mark = NULL;
>> +                       goto skip;
>>                 }
>>
>> -               iter_info.inode_mark = inode_mark;
>> -               iter_info.vfsmount_mark = vfsmount_mark;
>> -
>> -               if (inode_group && vfsmount_group) {
>> -                       int cmp = fsnotify_compare_groups(inode_group,
>> -                                                         vfsmount_group);
>> -                       if (cmp > 0) {
>> -                               inode_group = NULL;
>> +               if (inode_mark && vfsmount_mark) {
>> +                       int cmp = fsnotify_compare_groups(inode_mark->group,
>> +                                                         vfsmount_mark->group);
>> +                       if (cmp > 0)
>>                                 inode_mark = NULL;
>> -                       } else if (cmp < 0) {
>> -                               vfsmount_group = NULL;
>> +                       else if (cmp < 0)
>>                                 vfsmount_mark = NULL;
>> -                       }
>>                 }
>>
>>                 ret = send_to_group(to_tell, inode_mark, vfsmount_mark, mask,
>> @@ -361,14 +353,11 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
>>
>>                 if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
>>                         goto out;
>> -skip_inode:
>> -               if (inode_group)
>> -                       inode_node = srcu_dereference(inode_node->next,
>> -                                                     &fsnotify_mark_srcu);
>> -skip_vfsmount:
>> -               if (vfsmount_group)
>> -                       vfsmount_node = srcu_dereference(vfsmount_node->next,
>> -                                                        &fsnotify_mark_srcu);
>> +skip:
>> +               if (inode_mark)
>> +                       iter_info.inode_mark = fsnotify_next_mark(iter_info.inode_mark);
> else if?

We can have both (see  fsnotify_compare_groups()).

>> +               if (vfsmount_mark)
>> +                       iter_info.vfsmount_mark = fsnotify_next_mark(iter_info.vfsmount_mark);
>>         }
>>         ret = 0;
>>  out:
>> --
>> 2.5.5
>>



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