This is a note to let you know that I've just added the patch titled
btrfs: fix processing of delayed data refs during backref walking
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-fix-processing-of-delayed-data-refs-during-bac.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 991194e6de9c7646460c3e847e3bada2f5a08b5b
Author: Filipe Manana <fdmanana@xxxxxxxx>
Date: Tue Oct 11 13:16:51 2022 +0100
btrfs: fix processing of delayed data refs during backref walking
[ Upstream commit 4fc7b57228243d09c0d878873bf24fa64a90fa01 ]
When processing delayed data references during backref walking and we are
using a share context (we are being called through fiemap), whenever we
find a delayed data reference for an inode different from the one we are
interested in, then we immediately exit and consider the data extent as
shared. This is wrong, because:
1) This might be a DROP reference that will cancel out a reference in the
extent tree;
2) Even if it's an ADD reference, it may be followed by a DROP reference
that cancels it out.
In either case we should not exit immediately.
Fix this by never exiting when we find a delayed data reference for
another inode - instead add the reference and if it does not cancel out
other delayed reference, we will exit early when we call
extent_is_shared() after processing all delayed references. If we find
a drop reference, then signal the code that processes references from
the extent tree (add_inline_refs() and add_keyed_refs()) to not exit
immediately if it finds there a reference for another inode, since we
have delayed drop references that may cancel it out. In this later case
we exit once we don't have references in the rb trees that cancel out
each other and have two references for different inodes.
Example reproducer for case 1):
$ cat test-1.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
mkfs.btrfs -f $DEV
mount $DEV $MNT
xfs_io -f -c "pwrite 0 64K" $MNT/foo
cp --reflink=always $MNT/foo $MNT/bar
echo
echo "fiemap after cloning:"
xfs_io -c "fiemap -v" $MNT/foo
rm -f $MNT/bar
echo
echo "fiemap after removing file bar:"
xfs_io -c "fiemap -v" $MNT/foo
umount $MNT
Running it before this patch, the extent is still listed as shared, it has
the flag 0x2000 (FIEMAP_EXTENT_SHARED) set:
$ ./test-1.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
Example reproducer for case 2):
$ cat test-2.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
mkfs.btrfs -f $DEV
mount $DEV $MNT
xfs_io -f -c "pwrite 0 64K" $MNT/foo
cp --reflink=always $MNT/foo $MNT/bar
# Flush delayed references to the extent tree and commit current
# transaction.
sync
echo
echo "fiemap after cloning:"
xfs_io -c "fiemap -v" $MNT/foo
rm -f $MNT/bar
echo
echo "fiemap after removing file bar:"
xfs_io -c "fiemap -v" $MNT/foo
umount $MNT
Running it before this patch, the extent is still listed as shared, it has
the flag 0x2000 (FIEMAP_EXTENT_SHARED) set:
$ ./test-2.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
After this patch, after deleting bar in both tests, the extent is not
reported with the 0x2000 flag anymore, it gets only the flag 0x1
(which is FIEMAP_EXTENT_LAST):
$ ./test-1.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x1
$ ./test-2.sh
fiemap after cloning:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x2001
fiemap after removing file bar:
/mnt/sdj/foo:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..127]: 26624..26751 128 0x1
These tests will later be converted to a test case for fstests.
Fixes: dc046b10c8b7d4 ("Btrfs: make fiemap not blow when you have lots of snapshots")
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index baff31a147e7..7e8fac12f3f8 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -137,6 +137,7 @@ struct share_check {
u64 root_objectid;
u64 inum;
int share_count;
+ bool have_delayed_delete_refs;
};
static inline int extent_is_shared(struct share_check *sc)
@@ -881,13 +882,22 @@ static int add_delayed_refs(const struct btrfs_fs_info *fs_info,
key.offset = ref->offset;
/*
- * Found a inum that doesn't match our known inum, we
- * know it's shared.
+ * If we have a share check context and a reference for
+ * another inode, we can't exit immediately. This is
+ * because even if this is a BTRFS_ADD_DELAYED_REF
+ * reference we may find next a BTRFS_DROP_DELAYED_REF
+ * which cancels out this ADD reference.
+ *
+ * If this is a DROP reference and there was no previous
+ * ADD reference, then we need to signal that when we
+ * process references from the extent tree (through
+ * add_inline_refs() and add_keyed_refs()), we should
+ * not exit early if we find a reference for another
+ * inode, because one of the delayed DROP references
+ * may cancel that reference in the extent tree.
*/
- if (sc && sc->inum && ref->objectid != sc->inum) {
- ret = BACKREF_FOUND_SHARED;
- goto out;
- }
+ if (sc && count < 0)
+ sc->have_delayed_delete_refs = true;
ret = add_indirect_ref(fs_info, preftrees, ref->root,
&key, 0, node->bytenr, count, sc,
@@ -917,7 +927,7 @@ static int add_delayed_refs(const struct btrfs_fs_info *fs_info,
}
if (!ret)
ret = extent_is_shared(sc);
-out:
+
spin_unlock(&head->lock);
return ret;
}
@@ -1020,7 +1030,8 @@ static int add_inline_refs(const struct btrfs_fs_info *fs_info,
key.type = BTRFS_EXTENT_DATA_KEY;
key.offset = btrfs_extent_data_ref_offset(leaf, dref);
- if (sc && sc->inum && key.objectid != sc->inum) {
+ if (sc && sc->inum && key.objectid != sc->inum &&
+ !sc->have_delayed_delete_refs) {
ret = BACKREF_FOUND_SHARED;
break;
}
@@ -1030,6 +1041,7 @@ static int add_inline_refs(const struct btrfs_fs_info *fs_info,
ret = add_indirect_ref(fs_info, preftrees, root,
&key, 0, bytenr, count,
sc, GFP_NOFS);
+
break;
}
default:
@@ -1119,7 +1131,8 @@ static int add_keyed_refs(struct btrfs_fs_info *fs_info,
key.type = BTRFS_EXTENT_DATA_KEY;
key.offset = btrfs_extent_data_ref_offset(leaf, dref);
- if (sc && sc->inum && key.objectid != sc->inum) {
+ if (sc && sc->inum && key.objectid != sc->inum &&
+ !sc->have_delayed_delete_refs) {
ret = BACKREF_FOUND_SHARED;
break;
}
@@ -1542,6 +1555,7 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr,
.root_objectid = root->root_key.objectid,
.inum = inum,
.share_count = 0,
+ .have_delayed_delete_refs = false,
};
ulist_init(roots);
@@ -1576,6 +1590,7 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr,
break;
bytenr = node->val;
shared.share_count = 0;
+ shared.have_delayed_delete_refs = false;
cond_resched();
}
