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. > Will test it out though... > > Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Thanks. BTW, will you pick up these patches please? 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
