On Wed, Apr 30, 2014 at 10:12:06PM +0100, Al Viro wrote: > On Wed, Apr 30, 2014 at 01:57:05PM -0700, Linus Torvalds wrote: > > On Wed, Apr 30, 2014 at 1:38 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > We do not (and cannot) call dentry_kill() with rcu_read_lock held - it can > > > trigger any amount of IO, for one thing. We can take it around the > > > couple of places where do that spin_unlock(&dentry->d_lock) (along with > > > setting DCACHE_RCUACCESS) - that's what I'd been refering to. > > > > Just the last spin_unlock() would be the case that matters, if the > > spin_unlock() is done on something that could be freed immediately and > > the lock protects and is inside the entity that gets freed. > > *nod* > > There are two such spin_unlock (handover from shrink_dentry_list() to > dput() and the opposite one), but they are all that needs protection - > ->d_flags update is outside the rcu-critical area. I really wonder > if we *can* get there without DCACHE_RCUACCESS having been set, though; > dentry would have to be > * picked into shrink list (i.e. have had zero refcount at some point) > * never had been through __d_rehash() > shrink_dentry_list() definitely counts on that being impossible, and it > probably is, but I'm feeling seriously paranoid about the whole area. > I'll finish grepping through the tree and probably drop setting > DCACHE_RCUACCESS from the patch - either that, or set it in d_shrink_add() > it it turns out that it is possible and shrink_dentry_list() is fucked... OK, it really can't happen. The proof is more convoluted than I'd like it, but it's solid enough, so setting that flag in dentry_kill() handover cases wasn't needed. I've just pushed the whole thing to vfs.git#for-linus; review and testing would be very welcome. I can repost it one more time, but the only difference compared to the last variant in this thread is not bothering with DCACHE_RCUACCESS. It has survived LTP tests, going through xfstests now... -- 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
