On Fri 23-12-16 07:48:43, Amir Goldstein wrote: > On Thu, Dec 22, 2016 at 11:15 AM, Jan Kara <jack@xxxxxxx> wrote: > > Currently notification marks are attached to object (inode or vfsmnt) by > > a hlist_head in the object. The list is also protected by a spinlock in > > the object. So while there is any mark attached to the list of marks, > > the object must be pinned in memory (and thus e.g. last iput() deleting > > inode cannot happen). Also for list iteration in fsnotify() to work, we > > must hold fsnotify_mark_srcu lock so that mark itself and > > mark->obj_list.next cannot get freed. Thus we are required to wait for > > response to fanotify events from userspace process with > > fsnotify_mark_srcu lock held. That causes issues when userspace process > > is buggy and does not reply to some event - basically the whole > > notification subsystem gets eventually stuck. > > > > So to be able to drop fsnotify_mark_srcu lock while waiting for > > response, we have to pin the mark in memory and make sure it stays in > > the object list (as removing the mark waiting for response could lead to > > lost notification events for groups later in the list). However we don't > > want inode reclaim to block on such mark as that would lead to system > > just locking up elsewhere. > > > > This commit tries to pave a way towards solving these conflicting > > lifetime needs. Instead of anchoring the list of marks directly in the > > object, we anchor it in a dedicated structure (fsnotify_mark_list) and > > just point to that structure from the object. Also the list is protected > > by a spinlock contained in that structure. With this, we can detach > > notification marks from object without having to modify the list itself. > > > > The structural change looks very good to. > It makes the code much easier to manage IMO. > > I am only half way though this big change, but I wanted to make one meta > comment. > > I have a problem with the choice of naming for the new struct. > 'list' is really an overloaded term and the use of 'list' as a name of > a class that > contains a list head makes for some really confusing constructs like > list->list and mark->obj_list_head which is not a list_head struct. OK, I'll think about better naming. I agree it may be slightly confusing. > For future generations, I suggest that we invest the effort in choosing > a name that makes more sense. I do realize how annoying it would be to > fix the entire series now, so it's not a problem if renaming is done in the end > of the series as long as we agree on the end result. > > May I suggest the name fsnotify_tap to describe the new struct. > I know it is arbitrary, but not more arbitrary then fsnotify_mark and certainly > not any more arbitrary then fsnotify_group. > > Here are some examples of constructs that will make more sense: > > <+#define FSNOTIFY_LIST_TYPE_INODE 0x01 > <+#define FSNOTIFY_LIST_TYPE_VFSMOUNT 0x02 > >+#define FSNOTIFY_TAP_TYPE_INODE 0x01 > >+#define FSNOTIFY_TAP_TYPE_VFSMOUNT 0x02 > > LIST_TYPE_INODE implies this is a list of inodes > TAP_TYPE_INODE implies this is a tap on an inode Frankly, I don't like 'TAP' much because as you say it is rather arbitrary (or maybe I'm just missing a point as a non-native speaker). I'd prefer something more descriptive. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
