On Mon, Jun 3, 2019 at 4:22 PM Jan Kara <jack@xxxxxxx> wrote: > > Hole puching currently evicts pages from page cache and then goes on to > remove blocks from the inode. This happens under both i_mmap_sem and > i_rwsem held exclusively which provides appropriate serialization with > racing page faults. However there is currently nothing that prevents > ordinary read(2) from racing with the hole punch and instantiating page > cache page after hole punching has evicted page cache but before it has > removed blocks from the inode. This page cache page will be mapping soon > to be freed block and that can lead to returning stale data to userspace > or even filesystem corruption. > > Fix the problem by protecting reads as well as readahead requests with > i_mmap_sem. > So ->write_iter() does not take i_mmap_sem right? and therefore mixed randrw workload is not expected to regress heavily because of this change? Did you test performance diff? Here [1] I posted results of fio test that did x5 worse in xfs vs. ext4, but I've seen much worse cases. Thanks, Amir. [1] https://lore.kernel.org/linux-fsdevel/CAOQ4uxhu=Qtme9RJ7uZXYXt0UE+=xD+OC4gQ9EYkDC1ap8Hizg@xxxxxxxxxxxxxx/
