On Fri, Aug 30, 2019 at 05:24:49PM +0200, 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. <nod> I imgaine this race was hard to spot in the first place... > > Will test it out though... > > > > Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > Thanks. BTW, will you pick up these patches please? Yeah, they looked fine. --D > Honza > > > > > --D > > > > > --- > > > fs/xfs/xfs_file.c | 26 ++++++++++++++++++++++++++ > > > 1 file changed, 26 insertions(+) > > > > > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > > > index 28101bbc0b78..d952d5962e93 100644 > > > --- a/fs/xfs/xfs_file.c > > > +++ b/fs/xfs/xfs_file.c > > > @@ -28,6 +28,7 @@ > > > #include <linux/falloc.h> > > > #include <linux/backing-dev.h> > > > #include <linux/mman.h> > > > +#include <linux/fadvise.h> > > > > > > static const struct vm_operations_struct xfs_file_vm_ops; > > > > > > @@ -933,6 +934,30 @@ xfs_file_fallocate( > > > return error; > > > } > > > > > > +STATIC int > > > +xfs_file_fadvise( > > > + struct file *file, > > > + loff_t start, > > > + loff_t end, > > > + int advice) > > > +{ > > > + struct xfs_inode *ip = XFS_I(file_inode(file)); > > > + int ret; > > > + int lockflags = 0; > > > + > > > + /* > > > + * Operations creating pages in page cache need protection from hole > > > + * punching and similar ops > > > + */ > > > + if (advice == POSIX_FADV_WILLNEED) { > > > + lockflags = XFS_IOLOCK_SHARED; > > > + xfs_ilock(ip, lockflags); > > > + } > > > + ret = generic_fadvise(file, start, end, advice); > > > + if (lockflags) > > > + xfs_iunlock(ip, lockflags); > > > + return ret; > > > +} > > > > > > STATIC loff_t > > > xfs_file_remap_range( > > > @@ -1232,6 +1257,7 @@ const struct file_operations xfs_file_operations = { > > > .fsync = xfs_file_fsync, > > > .get_unmapped_area = thp_get_unmapped_area, > > > .fallocate = xfs_file_fallocate, > > > + .fadvise = xfs_file_fadvise, > > > .remap_file_range = xfs_file_remap_range, > > > }; > > > > > > -- > > > 2.16.4 > > > > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR
