linux-kernel - Re: [PATCH 2/4] fs/block_dev: always invalidate cleancache in invalidate

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Message-ID: <b2c72883-d9a2-bfda-2cd3-ae9475922bc5@virtuozzo.com>
Date:   Wed, 19 Apr 2017 16:22:42 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Nikolay Borisov <n.borisov.lkml@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        <linux-fsdevel@...r.kernel.org>
CC:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        Steve French <sfrench@...ba.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>,
        Johannes Weiner <hannes@...xchg.org>,
        Alexey Kuznetsov <kuznet@...tuozzo.com>,
        Christoph Hellwig <hch@....de>,
        <v9fs-developer@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <linux-cifs@...r.kernel.org>,
        <samba-technical@...ts.samba.org>, <linux-nfs@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [PATCH 2/4] fs/block_dev: always invalidate cleancache in
 invalidate_bdev()

On 04/18/2017 09:51 PM, Nikolay Borisov wrote:
> 
> 
> On 14.04.2017 17:07, Andrey Ryabinin wrote:
>> invalidate_bdev() calls cleancache_invalidate_inode() iff ->nrpages != 0
>> which doen't make any sense.
>> Make invalidate_bdev() always invalidate cleancache data.
>>
>> Fixes: c515e1fd361c ("mm/fs: add hooks to support cleancache")
>> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
>> ---
>>  fs/block_dev.c | 11 +++++------
>>  1 file changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index e405d8e..7af4787 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -103,12 +103,11 @@ void invalidate_bdev(struct block_device *bdev)
>>  {
>>  	struct address_space *mapping = bdev->bd_inode->i_mapping;
>>  
>> -	if (mapping->nrpages == 0)
>> -		return;
>> -
>> -	invalidate_bh_lrus();
>> -	lru_add_drain_all();	/* make sure all lru add caches are flushed */
>> -	invalidate_mapping_pages(mapping, 0, -1);
>> +	if (mapping->nrpages) {
>> +		invalidate_bh_lrus();
>> +		lru_add_drain_all();	/* make sure all lru add caches are flushed */
>> +		invalidate_mapping_pages(mapping, 0, -1);
>> +	}
> 
> How is this different than the current code? You will only invalidate
> the mapping iff ->nrpages > 0 ( I assume it can't go down below 0) ?

The difference is that invalidate_bdev() now always calls cleancache_invalidate_inode()
(you won't see it in this diff, it's placed after this if(mapping->nrpages){} block,)

> Perhaps just remove the if altogether?
> 

Given that invalidate_mapping_pages() invalidates exceptional entries as well, it certainly doesn't look
right that we look only at mapping->nrpages and completely ignore ->nrexceptional.
So maybe removing if() would be a right thing to do. But I think that should be a separate patch as it would
fix a another bug probably introduced by commit 91b0abe36a7b ("mm + fs: store shadow entries in page cache")

My intention here was to fix only cleancache case.


>>  	/* 99% of the time, we don't need to flush the cleancache on the bdev.
>>  	 * But, for the strange corners, lets be cautious
>>  	 */
>>