On Sat, Oct 07, 2017 at 02:56:40PM +0300, Vladimir Davydov wrote: > Hello, > > On Fri, Oct 06, 2017 at 11:06:04AM +0200, Michal Hocko wrote: > > On Fri 06-10-17 16:59:18, Jia-Ju Bai wrote: > > > According to fs/super.c, the kernel may sleep under a spinlock. > > > The function call path is: > > > put_super (acquire the spinlock) > > > __put_super > > > destroy_super > > > list_lru_destroy > > > list_lru_unregister > > > mutex_lock --> may sleep > > > memcg_get_cache_ids > > > down_read --> may sleep > > > > > > This bug is found by my static analysis tool and my code review. > > This is false-positive: by the time we get to destroy_super(), the lru > lists have already been destroyed - see deactivate_locked_super() - so > list_lru_destroy() will retrun right away without attempting to take any > locks. That's why there's no lockdep warnings regarding this issue. > > I think we can move list_lru_destroy() to destroy_super_work() to > suppress this warning. Not sure if it's really worth the trouble though. It's a bit trickier than that (callers of destroy_super() prior to superblock getting reachable via shared data structures do not have that lru_list_destroy() a no-op, but they are not called under spinlocks). Locking in mm/list_lru.c looks excessive, but then I'm not well familiar with that code.
