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Subject: Re: [PATCH] fs: Handle I_DONTCACHE in iput_final() instead of
 generic_drop_inode()
To:     Ira Weiny <ira.weiny@intel.com>
CC:     <viro@zeniv.linux.org.uk>, <david@fromorbit.com>,
        <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-xfs@vger.kernel.org>, <y-goto@fujitsu.com>
References: <20200831101313.168889-1-lihao2018.fnst@cn.fujitsu.com>
 <20200831171257.GF1422350@iweiny-DESK2.sc.intel.com>
From:   "Li, Hao" <lihao2018.fnst@cn.fujitsu.com>
Message-ID: <db5d145a-3b63-48db-6bd2-eb1d91323697@cn.fujitsu.com>
Date:   Tue, 1 Sep 2020 11:48:21 +0800
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On 2020/9/1 1:12, Ira Weiny wrote:
> 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@cn.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")

Yeah, this is more meaningful.

I'm not sure if I need to submit a v2 patch, or this tag will be added
by the maintainer when applying this patch. I have no experience with
this before. Thanks!

Regards,
Hao Li

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