| Message ID | 20210209173337.16621-1-marek.behun@nic.cz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [u-boot] fs: btrfs: do not fail when offset of a ROOT_ITEM is not -1 | expand |
On 2021/2/10 上午1:33, Marek Behún wrote: > When the btrfs_read_fs_root() function is searching a ROOT_ITEM with > location key offset other than -1, it currently fails via BUG_ON. > > The offset can have other value than -1, though. This can happen for > example if a subvolume is renamed: > > $ btrfs subvolume create X && sync > Create subvolume './X' > $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: X$ > location key (270 ROOT_ITEM 18446744073709551615) type DIR > transid 283 data_len 0 name_len 1 > name: X > $ mv X Y && sync > $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: Y$ > location key (270 ROOT_ITEM 0) type DIR > transid 285 data_len 0 name_len 1 > name: Y > > As can be seen the offset changed from -1ULL to 0. Offset for subvolume ROOT_ITEM can be other values, especially for snapshot that offset is the transid when it get created. But the problem is, if we call btrfs_read_fs_root() for subvolume tree, the offset of the key really doesn't matter, the only important thing is the objectid. Thus we use that BUG_ON() to catch careless callers. Would you please provide a case where we wrongly call btrfs_read_fs_root() with incorrect offset inside btrfs-progs/uboot? I believe that would be the proper way to fix. Thanks, Qu > > Do not fail in this case. > > Signed-off-by: Marek Behún <marek.behun@nic.cz> > Cc: David Sterba <dsterba@suse.com> > Cc: Qu Wenruo <wqu@suse.com> > Cc: Tom Rini <trini@konsulko.com> > --- > fs/btrfs/disk-io.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index b332ecb796..c6fdec95c1 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -732,8 +732,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info, > return fs_info->chunk_root; > if (location->objectid == BTRFS_CSUM_TREE_OBJECTID) > return fs_info->csum_root; > - BUG_ON(location->objectid == BTRFS_TREE_RELOC_OBJECTID || > - location->offset != (u64)-1); > + BUG_ON(location->objectid == BTRFS_TREE_RELOC_OBJECTID); > > node = rb_search(&fs_info->fs_root_tree, (void *)&objectid, > btrfs_fs_roots_compare_objectids, NULL); >
On Wed, 10 Feb 2021 08:09:14 +0800 Qu Wenruo <quwenruo.btrfs@gmx.com> wrote: > On 2021/2/10 上午1:33, Marek Behún wrote: > > When the btrfs_read_fs_root() function is searching a ROOT_ITEM with > > location key offset other than -1, it currently fails via BUG_ON. > > > > The offset can have other value than -1, though. This can happen for > > example if a subvolume is renamed: > > > > $ btrfs subvolume create X && sync > > Create subvolume './X' > > $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: X$ > > location key (270 ROOT_ITEM 18446744073709551615) type DIR > > transid 283 data_len 0 name_len 1 > > name: X > > $ mv X Y && sync > > $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: Y$ > > location key (270 ROOT_ITEM 0) type DIR > > transid 285 data_len 0 name_len 1 > > name: Y > > > > As can be seen the offset changed from -1ULL to 0. > > > Offset for subvolume ROOT_ITEM can be other values, especially for > snapshot that offset is the transid when it get created. > > But the problem is, if we call btrfs_read_fs_root() for subvolume tree, > the offset of the key really doesn't matter, the only important thing is > the objectid. > > Thus we use that BUG_ON() to catch careless callers. > > Would you please provide a case where we wrongly call > btrfs_read_fs_root() with incorrect offset inside btrfs-progs/uboot? > > I believe that would be the proper way to fix. Qu, this can be triggered in U-Boot when listing a directory containing a subvolume that was renamed: - create a subvolume && sync - rename subvolume && sync - umount, reboot, list the directory containing the subvolume in u-boot It will also break when you want to read a file that has a subvolume in it's path (e.g. `read mmc 0 0x10000000 /renamed-subvol/file`). I found out this btrfs-progs commit: https://github.com/kdave/btrfs-progs/commit/10f1af0fe7de5a0310657993c7c21a1d78087e56 This commit ensures that while searching a directory recursively, when a ROOT_ITEM is encountered, the offset of its location is changed to -1 before passing the location to btrfs_read_fs_root(). So maybe we could do this in u-boot as well, but why do this? Linux' btrfs driver does not check whether the offset is -1. So why do it here? BTW, Qu, I think we have to change the BUG_ON code in U-Boot's btrfs driver. BUG_ON in U-Boot calls a complete SOC reset. We can't break whole U-Boot simply because btrfs partition contains broken data. U-Boot commands must fail in such a case, not reset the SOC. Marek
On 2021/2/10 上午9:05, Marek Behun wrote: > On Wed, 10 Feb 2021 08:09:14 +0800 > Qu Wenruo <quwenruo.btrfs@gmx.com> wrote: > >> On 2021/2/10 上午1:33, Marek Behún wrote: >>> When the btrfs_read_fs_root() function is searching a ROOT_ITEM with >>> location key offset other than -1, it currently fails via BUG_ON. >>> >>> The offset can have other value than -1, though. This can happen for >>> example if a subvolume is renamed: >>> >>> $ btrfs subvolume create X && sync >>> Create subvolume './X' >>> $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: X$ >>> location key (270 ROOT_ITEM 18446744073709551615) type DIR >>> transid 283 data_len 0 name_len 1 >>> name: X >>> $ mv X Y && sync >>> $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: Y$ >>> location key (270 ROOT_ITEM 0) type DIR >>> transid 285 data_len 0 name_len 1 >>> name: Y >>> >>> As can be seen the offset changed from -1ULL to 0. >> >> >> Offset for subvolume ROOT_ITEM can be other values, especially for >> snapshot that offset is the transid when it get created. >> >> But the problem is, if we call btrfs_read_fs_root() for subvolume tree, >> the offset of the key really doesn't matter, the only important thing is >> the objectid. >> >> Thus we use that BUG_ON() to catch careless callers. >> >> Would you please provide a case where we wrongly call >> btrfs_read_fs_root() with incorrect offset inside btrfs-progs/uboot? >> >> I believe that would be the proper way to fix. > > Qu, > > this can be triggered in U-Boot when listing a directory containing a > subvolume that was renamed: > - create a subvolume && sync > - rename subvolume && sync > - umount, reboot, list the directory containing the subvolume in > u-boot > It will also break when you want to read a file that has a subvolume in > it's path (e.g. `read mmc 0 0x10000000 /renamed-subvol/file`). > > I found out this btrfs-progs commit: > https://github.com/kdave/btrfs-progs/commit/10f1af0fe7de5a0310657993c7c21a1d78087e56 > This commit ensures that while searching a directory recursively, when > a ROOT_ITEM is encountered, the offset of its location is changed to -1 > before passing the location to btrfs_read_fs_root(). That's what I expect the code to do, but you're right, if kernel is not doing it anymore, I prefer the kernel behavior. > > So maybe we could do this in u-boot as well, but why do this? Linux' > btrfs driver does not check whether the offset is -1. So why do it here? You're correct, the kernel is using new schema, btrfs_get_fs_root(), which only requires root objectid and completely get rid of the offset/type, which is far less possible to call with wrong parameters. It would be a good timing to sync the code between kernel and progs/u-boot now. > > BTW, Qu, I think we have to change the BUG_ON code in U-Boot's btrfs > driver. BUG_ON in U-Boot calls a complete SOC reset. We can't break > whole U-Boot simply because btrfs partition contains broken data. > U-Boot commands must fail in such a case, not reset the SOC. Well, progs (and even kernel) is a mine-field for BUG_ON()s. But at least for kernel, it's protected by tree-checker which rejects invalid on-disk data before it reaches btrfs code, thus mostly kernel BUG_ON()s are really hard to hit (a lot of them are even impossible to hit after the introduction of tree-checker), and indicate real problems. For now, the BUG_ON()s in U-boot still indicates problems that we can't really solve or doesn't expect at all in btrfs realm, e.g. the BUG_ON() you're hitting (call sites problem). I admit it's a pain in the ass for full SoC reset, but I don't have any better alternatives yet. The mid to long term solution would be introducing tree-checker to U-boot, so that the remaining BUG_ON()s are really code bugs. Thanks, Qu > > Marek >
On Wed, 10 Feb 2021 09:20:11 +0800 Qu Wenruo <wqu@suse.com> wrote: > You're correct, the kernel is using new schema, btrfs_get_fs_root(), > which only requires root objectid and completely get rid of the > offset/type, which is far less possible to call with wrong parameters. > > It would be a good timing to sync the code between kernel and > progs/u-boot now. So do you agree with this patch? If so, can you add Reviewed-by? Thanks.
On 2021/2/11 上午12:21, Marek Behun wrote: > On Wed, 10 Feb 2021 09:20:11 +0800 > Qu Wenruo <wqu@suse.com> wrote: > >> You're correct, the kernel is using new schema, btrfs_get_fs_root(), >> which only requires root objectid and completely get rid of the >> offset/type, which is far less possible to call with wrong parameters. >> >> It would be a good timing to sync the code between kernel and >> progs/u-boot now. > > So do you agree with this patch? If so, can you add Reviewed-by? Thanks. > I mean, to change btrfs-progs interface to follow kernel btrfs_get_fs_root() schema, just pass objectid, without the need for btrfs_key. Thanks, Qu
On Tue, Feb 09, 2021 at 06:33:37PM +0100, Marek Behún wrote: > When the btrfs_read_fs_root() function is searching a ROOT_ITEM with > location key offset other than -1, it currently fails via BUG_ON. > > The offset can have other value than -1, though. This can happen for > example if a subvolume is renamed: > > $ btrfs subvolume create X && sync > Create subvolume './X' > $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: X$ > location key (270 ROOT_ITEM 18446744073709551615) type DIR > transid 283 data_len 0 name_len 1 > name: X > $ mv X Y && sync > $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: Y$ > location key (270 ROOT_ITEM 0) type DIR > transid 285 data_len 0 name_len 1 > name: Y > > As can be seen the offset changed from -1ULL to 0. > > Do not fail in this case. > > Signed-off-by: Marek Behún <marek.behun@nic.cz> > Cc: David Sterba <dsterba@suse.com> > Cc: Qu Wenruo <wqu@suse.com> > Cc: Tom Rini <trini@konsulko.com> Applied to u-boot/master, thanks!
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index b332ecb796..c6fdec95c1 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -732,8 +732,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info, return fs_info->chunk_root; if (location->objectid == BTRFS_CSUM_TREE_OBJECTID) return fs_info->csum_root; - BUG_ON(location->objectid == BTRFS_TREE_RELOC_OBJECTID || - location->offset != (u64)-1); + BUG_ON(location->objectid == BTRFS_TREE_RELOC_OBJECTID); node = rb_search(&fs_info->fs_root_tree, (void *)&objectid, btrfs_fs_roots_compare_objectids, NULL);
When the btrfs_read_fs_root() function is searching a ROOT_ITEM with location key offset other than -1, it currently fails via BUG_ON. The offset can have other value than -1, though. This can happen for example if a subvolume is renamed: $ btrfs subvolume create X && sync Create subvolume './X' $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: X$ location key (270 ROOT_ITEM 18446744073709551615) type DIR transid 283 data_len 0 name_len 1 name: X $ mv X Y && sync $ btrfs inspect-internal dump-tree /dev/root | grep -B 2 'name: Y$ location key (270 ROOT_ITEM 0) type DIR transid 285 data_len 0 name_len 1 name: Y As can be seen the offset changed from -1ULL to 0. Do not fail in this case. Signed-off-by: Marek Behún <marek.behun@nic.cz> Cc: David Sterba <dsterba@suse.com> Cc: Qu Wenruo <wqu@suse.com> Cc: Tom Rini <trini@konsulko.com> --- fs/btrfs/disk-io.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)