| Message ID | 28e3e02ed14fe7c0859707e1a10a447fe4338c16.1648535838.git.naohiro.aota@wdc.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | protect relocation with sb_start_write | expand |
On Tue, Mar 29, 2022 at 03:56:00PM +0900, Naohiro Aota wrote: > Relocation of a data block group creates ordered extents. They can cause a > hang when a process is trying to thaw the filesystem. > > We should have called sb_start_write(), so the filesystem is not being > frozen. Add an ASSERT to check it is protected. > > Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com> > --- > fs/btrfs/relocation.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c > index fdc2c4b411f0..5e52cd8d5f23 100644 > --- a/fs/btrfs/relocation.c > +++ b/fs/btrfs/relocation.c > @@ -3977,6 +3977,16 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start) > if (!bg) > return -ENOENT; > > + /* > + * Relocation of a data block group creates ordered extents. > + * Without sb_start_write(), we can freeze the FS while unfinished > + * ordered extents are left. Such ordered extents can cause a > + * deadlock e.g, when syncfs() is trying to finish them because syncfs() is not trying to finish them, it's waiting for them to complete. > + * they never finish as the FS is already frozen. More specifically they can't finish because they block when joining a transaction, due to the fact that the freeze locks are being held in write mode. Anyway, I won't make you send yet another version. Perhaps this is something David can fixup when he picks the patch. Reviewed-by: Filipe Manana <fdmanana@suse.com> Thanks. > + */ > + if (bg->flags & BTRFS_BLOCK_GROUP_DATA) > + ASSERT(sb_write_started(fs_info->sb)); > + > if (btrfs_pinned_by_swapfile(fs_info, bg)) { > btrfs_put_block_group(bg); > return -ETXTBSY; > -- > 2.35.1 >
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index fdc2c4b411f0..5e52cd8d5f23 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -3977,6 +3977,16 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start) if (!bg) return -ENOENT; + /* + * Relocation of a data block group creates ordered extents. + * Without sb_start_write(), we can freeze the FS while unfinished + * ordered extents are left. Such ordered extents can cause a + * deadlock e.g, when syncfs() is trying to finish them because + * they never finish as the FS is already frozen. + */ + if (bg->flags & BTRFS_BLOCK_GROUP_DATA) + ASSERT(sb_write_started(fs_info->sb)); + if (btrfs_pinned_by_swapfile(fs_info, bg)) { btrfs_put_block_group(bg); return -ETXTBSY;
Relocation of a data block group creates ordered extents. They can cause a hang when a process is trying to thaw the filesystem. We should have called sb_start_write(), so the filesystem is not being frozen. Add an ASSERT to check it is protected. Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com> --- fs/btrfs/relocation.c | 10 ++++++++++ 1 file changed, 10 insertions(+)