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

[Kirill Korotaev]

> > <<<< 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

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