Re: [PATCH] shrink_dcache_parent() races against shrink_dcache_memory()

[Kirill Korotaev <dev@sw.ru>]

>><<<< and here, when you drop sb_lock, and dentry->d_lock/dcache_lock in 
>>prune_dentry() it looks to me that we have exactly the same situation as 
>>it was without your patch:
>><<<< another CPU can start umount in parallel.
>><<<< maybe sb_lock barrier helps this somehow, but I can't see how yet...
> 
>>From the unmount path, __mntput() is called. It sets s_active to 0 in
> deactivate_super(), hence our check would prevent us from pruning a dentry
> that is a part of a super block that is going to go away soon. The idea
> is to let the unmount do all the work here, the allocator can concentrate
> on other dentries.
you check can happen 1 nanosecond before it sets s_active, after that 
the code goes into prune_dentry(), while deactivate_super() successfully 
sets s_active and starts umount main job. Nothing prevents the race... :(

Kirill