Re: [PATCH v2 1/1] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

["David Hildenbrand (Red Hat)" <david@kernel.org>]

On 1/3/26 19:03, Andrew Morton wrote:
> On Sun, 14 Dec 2025 19:00:43 -0800 Joanne Koong <joannelkoong@gmail.com> wrote:
> 
>> Skip waiting on writeback for inodes that belong to mappings that do not
>> have data integrity guarantees (denoted by the AS_NO_DATA_INTEGRITY
>> mapping flag).
>>
>> This restores fuse back to prior behavior where syncs are no-ops. This
>> is needed because otherwise, if a system is running a faulty fuse
>> server that does not reply to issued write requests, this will cause
>> wait_sb_inodes() to wait forever.
>>
>> Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree")
>> Reported-by: Athul Krishna <athul.krishna.kr@protonmail.com>
>> Reported-by: J. Neuschäfer <j.neuschaefer@gmx.net>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
>>
>> ..
>>
>> --- a/fs/fs-writeback.c
>> +++ b/fs/fs-writeback.c
>> @@ -2751,7 +2751,8 @@ static void wait_sb_inodes(struct super_block *sb)
>>   		 * do not have the mapping lock. Skip it here, wb completion
>>   		 * will remove it.
>>   		 */
>> -		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
>> +		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK) ||
>> +		    mapping_no_data_integrity(mapping))
>>   			continue;
> 
> It's not obvious why a no-data-integrity mapping would want to skip
> writeback - what do these things have to do with each other?
> 
> So can we please have a v2 which has a comment here explaining this to the
> reader?

Sorry for not replying earlier, I missed a couple of mails sent to my 
@redhat address due to @gmail being force-unsubscribed from linux-mm ...

Probably sufficient to add at the beginning of the commit:

"Above the while() loop in wait_sb_inodes(), we document that we must 
wait for all pages under writeback for data integrity. Consequently, if 
a mapping, like fuse, traditionally does not have data integrity 
semantics, there is no need to wait at all; we can simply skip these inodes.

So skip ..."

-- 
Cheers

David