On Wed, Sep 18, 2019 at 02:31:24PM +0200, Jan Kara wrote: > On Fri 30-08-19 17:24:49, Jan Kara wrote: > > On Thu 29-08-19 08:52:04, Darrick J. Wong wrote: > > > On Thu, Aug 29, 2019 at 03:10:34PM +0200, Jan Kara wrote: > > > > Hole puching currently evicts pages from page cache and then goes on to > > > > remove blocks from the inode. This happens under both XFS_IOLOCK_EXCL > > > > and XFS_MMAPLOCK_EXCL which provides appropriate serialization with > > > > racing reads or page faults. However there is currently nothing that > > > > prevents readahead triggered by fadvise() or madvise() from racing with > > > > the hole punch and instantiating page cache page after hole punching has > > > > evicted page cache in xfs_flush_unmap_range() 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 handling of readahead requests by > > > > XFS_IOLOCK_SHARED similarly as we protect reads. > > > > > > > > CC: stable@xxxxxxxxxxxxxxx > > > > Link: https://lore.kernel.org/linux-fsdevel/CAOQ4uxjQNmxqmtA_VbYW0Su9rKRk2zobJmahcyeaEVOFKVQ5dw@xxxxxxxxxxxxxx/ > > > > Reported-by: Amir Goldstein <amir73il@xxxxxxxxx> > > > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > > > > > Is there a test on xfstests to demonstrate this race? > > > > No, but I can try to create one. > > I was experimenting with this but I could not reproduce the issue in my > test VM without inserting artificial delay at appropriate place... So I > don't think there's much point in the fstest for this. <shrug> We've added debugging knobs to XFS that inject delays to demonstrate race conditions that are hard to reproduce, but OTOH it's more fun to have a generic/ test that you can use to convince the other fs maintainers to take your patches. :) --D > Honza > > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR
