Re: [PATCH, RFC] prune back iprune_sem

[Christoph Hellwig <hch@lst.de>]

ping?

On Tue, Nov 02, 2010 at 07:45:36PM +0100, 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.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index ae2727a..cfa7722 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -492,8 +492,6 @@ void evict_inodes(struct super_block *sb)
>  	struct inode *inode, *next;
>  	LIST_HEAD(dispose);
>  
> -	down_write(&iprune_sem);
> -
>  	spin_lock(&inode_lock);
>  	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
>  		if (atomic_read(&inode->i_count))
> @@ -518,6 +516,13 @@ void evict_inodes(struct super_block *sb)
>  	spin_unlock(&inode_lock);
>  
>  	dispose_list(&dispose);
> +
> +	/*
> +	 * Cycle through iprune_sem to make sure any inode that prune_icache
> +	 * moved off the list before we took the lock has been fully torn
> +	 * down.
> +	 */
> +	down_write(&iprune_sem);
>  	up_write(&iprune_sem);
>  }
>  
> @@ -534,8 +539,6 @@ int invalidate_inodes(struct super_block *sb)
>  	struct inode *inode, *next;
>  	LIST_HEAD(dispose);
>  
> -	down_write(&iprune_sem);
> -
>  	spin_lock(&inode_lock);
>  	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
>  		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE))
> @@ -559,7 +562,6 @@ int invalidate_inodes(struct super_block *sb)
>  	spin_unlock(&inode_lock);
>  
>  	dispose_list(&dispose);
> -	up_write(&iprune_sem);
>  
>  	return busy;
>  }
---end quoted text---