Re: [PATCH v6] fs: Fix page cache inconsistency when mixing buffered and AIO DIO

[Jeff Moyer <jmoyer@redhat.com>]

Jan Kara <jack@suse.cz> writes:

> On Thu 10-08-17 14:59:57, Lukas Czerner wrote:
>> Currently when mixing buffered reads and asynchronous direct writes it
>> is possible to end up with the situation where we have stale data in the
>> page cache while the new data is already written to disk. This is
>> permanent until the affected pages are flushed away. Despite the fact
>> that mixing buffered and direct IO is ill-advised it does pose a thread
>> for a data integrity, is unexpected and should be fixed.
>> 
>> Fix this by deferring completion of asynchronous direct writes to a
>> process context in the case that there are mapped pages to be found in
>> the inode. Later before the completion in dio_complete() invalidate
>> the pages in question. This ensures that after the completion the pages
>> in the written area are either unmapped, or populated with up-to-date
>> data. Also do the same for the iomap case which uses
>> iomap_dio_complete() instead.
>> 
>> This has a side effect of deferring the completion to a process context
>> for every AIO DIO that happens on inode that has pages mapped. However
>> since the consensus is that this is ill-advised practice the performance
>> implication should not be a problem.
>> 
>> This was based on proposal from Jeff Moyer, thanks!
>
> It seems the invalidation can be also removed from
> generic_file_direct_write(), can't it? It is duplicit there the same way as
> it was in the iomap code...

Yep, sure looks that way.

-Jeff