From: "Darrick J. Wong" <djwong@kernel.org> commit 2f4acd0fcd862e22eab45690ec2c08c80b6ef2e7 upstream. xfs_reflink_fill_{cow_hole,delalloc} are both presented with an inode, a data fork mapping, and a cow fork mapping. Unfortunately, these two helpers cycle the ILOCK to grab a transaction, which means that the mappings are stale as soon as we reacquire the ILOCK. Currently we refresh the cow fork mapping by re-calling xfs_find_trim_cow_extent, but we don't refresh the data fork mapping beforehand, which means that the xfs_bmap_trim_cow in that function queries the refcount btree about the wrong physical blocks and returns an inaccurate value in *shared. If *shared is now false, the directio write proceeds with a stale data fork mapping. Fix this by querying the data fork mapping if the sequence counter changes across the ILOCK cycle. Cc: hch@lst.de Cc: stable@vger.kernel.org # v4.11 Fixes: 3c68d44a2b49a0 ("xfs: allocate direct I/O COW blocks in iomap_begin") Signed-off-by: "Darrick J. Wong" <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Signed-off-by: Carlos Maiolino <cem@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Zizhi Wo <wozizhi@huaweicloud.com> --- fs/xfs/xfs_reflink.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index 5bf6682e701b..4d69280e3c17 100644 --- a/fs/xfs/xfs_reflink.c +++ b/fs/xfs/xfs_reflink.c @@ -390,6 +390,7 @@ xfs_reflink_fill_cow_hole( struct xfs_trans *tp; xfs_filblks_t resaligned; xfs_extlen_t resblks; + unsigned int seq_before = READ_ONCE(ip->i_df.if_seq); int nimaps; int error; bool found; @@ -408,6 +409,22 @@ xfs_reflink_fill_cow_hole( *lockmode = XFS_ILOCK_EXCL; + /* + * The data fork mapping may have changed while we dropped the ILOCK + * (a racing O_DIRECT writer under IOLOCK_SHARED can complete a full + * CoW cycle including xfs_reflink_end_cow(), which remaps this offset + * and drops the refcount of the old shared block). Re-read it so the + * shared-status recheck below and the caller's in-place iomap both + * operate on the current mapping rather than a stale physical block. + */ + if (seq_before != READ_ONCE(ip->i_df.if_seq)) { + nimaps = 1; + error = xfs_bmapi_read(ip, imap->br_startoff, + imap->br_blockcount, imap, &nimaps, 0); + if (error) + goto out_trans_cancel; + } + error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found); if (error || !*shared) goto out_trans_cancel; @@ -454,6 +471,8 @@ xfs_reflink_fill_delalloc( bool found; do { + unsigned int seq_before = READ_ONCE(ip->i_df.if_seq); + xfs_iunlock(ip, *lockmode); *lockmode = 0; @@ -464,6 +483,23 @@ xfs_reflink_fill_delalloc( *lockmode = XFS_ILOCK_EXCL; + /* + * The data fork mapping may have changed while we dropped the + * ILOCK (a racing O_DIRECT writer under IOLOCK_SHARED can + * complete a full CoW cycle including xfs_reflink_end_cow(), + * which remaps this offset and drops the refcount of the old + * shared block). Re-read it so the shared-status recheck + * below and the caller's in-place iomap both operate on the + * current mapping rather than a stale physical block. + */ + if (seq_before != READ_ONCE(ip->i_df.if_seq)) { + nimaps = 1; + error = xfs_bmapi_read(ip, imap->br_startoff, + imap->br_blockcount, imap, &nimaps, 0); + if (error) + goto out_trans_cancel; + } + error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found); if (error || !*shared) -- 2.52.0