Re: [PATCH, RFC] prune back iprune_sem

[Jan Kara <jack@suse.cz>]

On Tue 02-11-10 19:45:36, Christoph Hellwig wrote:
> iprune_sem is continously giving us lockdep warnings because we do take it in
> read mode in the reclaim path, but we're also doing non-NOFS allocations under
> it taken in write mode.
> 
> Taking a bit deeper look at it I think it's fixable quite trivially:
> 
>  - for invalidate_inodes we do not need iprune_sem at all.  We have an active
>    reference on the superblock, so the filesystem is not going away until it
>    has finished.
>  - for evict_inodes we do need it, to make sure prune_icache has done it's
>    work before we tear down the superblock.  But there is no reason to
>    hold it over the actual reclaim operation - it's enough to cycle through
>    it after the actual reclaim to make sure we wait for any pending
>    prune_icache to complete.
  The patch is OK but it's kind of subtle that evict_inodes() can now skip
some inode in the LRU list because prune_icache() is just processing it
and so it has elevated i_count. Everything will work out fine because
MS_ACTIVE is cleared and thus iput() will destroy the inode and
prune_icache() will then just continue with the next inode in the inode_lru
list. But as I said above it's subtle...

									Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR