linux-kernel - Re: [PATCH] fs: Handle I_DONTCACHE in iput_final() instead of generic_drop

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Message-ID: <20200831171257.GF1422350@iweiny-DESK2.sc.intel.com>
Date:   Mon, 31 Aug 2020 10:12:57 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Hao Li <lihao2018.fnst@...fujitsu.com>
Cc:     viro@...iv.linux.org.uk, david@...morbit.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, y-goto@...itsu.com
Subject: Re: [PATCH] fs: Handle I_DONTCACHE in iput_final() instead of
 generic_drop_inode()

On Mon, Aug 31, 2020 at 06:13:13PM +0800, Hao Li wrote:
> If generic_drop_inode() returns true, it means iput_final() can evict
> this inode regardless of whether it is dirty or not. If we check
> I_DONTCACHE in generic_drop_inode(), any inode with this bit set will be
> evicted unconditionally. This is not the desired behavior because
> I_DONTCACHE only means the inode shouldn't be cached on the LRU list.
> As for whether we need to evict this inode, this is what
> generic_drop_inode() should do. This patch corrects the usage of
> I_DONTCACHE.
> 
> This patch was proposed in [1].
> 
> [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/
> 
> Signed-off-by: Hao Li <lihao2018.fnst@...fujitsu.com>

Thanks!  I think this looks good, but shouldn't we add?  It seems like this is
a bug right?

Fixes: dae2f8ed7992 ("fs: Lift XFS_IDONTCACHE to the VFS layer")

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> ---
>  fs/inode.c         | 3 ++-
>  include/linux/fs.h | 3 +--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 72c4c347afb7..4e45d5ea3d0f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1625,7 +1625,8 @@ static void iput_final(struct inode *inode)
>  	else
>  		drop = generic_drop_inode(inode);
>  
> -	if (!drop && (sb->s_flags & SB_ACTIVE)) {
> +	if (!drop && !(inode->i_state & I_DONTCACHE) &&
> +			(sb->s_flags & SB_ACTIVE)) {
>  		inode_add_lru(inode);
>  		spin_unlock(&inode->i_lock);
>  		return;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e019ea2f1347..93caee80ce47 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2922,8 +2922,7 @@ extern int inode_needs_sync(struct inode *inode);
>  extern int generic_delete_inode(struct inode *inode);
>  static inline int generic_drop_inode(struct inode *inode)
>  {
> -	return !inode->i_nlink || inode_unhashed(inode) ||
> -		(inode->i_state & I_DONTCACHE);
> +	return !inode->i_nlink || inode_unhashed(inode);
>  }
>  extern void d_mark_dontcache(struct inode *inode);
>  
> -- 
> 2.28.0
> 
> 
>