From 342e5fcdb09b876e3b0d1f24272d452bc4a6ab7d Mon Sep 17 00:00:00 2001 From: Julian Sun Date: Wed, 11 Dec 2024 19:13:15 +0800 Subject: [PATCH] btrfs: fix transaction atomicity bug when enabling simple quotas set squota incompat bit before committing the transaction that enables the feature With the config CONFIG_BTRFS_ASSERT enabled, an assertion failure occurs regarding the simple quota feature. [ 5.596534] assertion failed: btrfs_fs_incompat(fs_info, SIMPLE_QUOTA), in fs/btrfs/qgroup.c:365 [ 5.597098] ------------[ cut here ]------------ [ 5.597371] kernel BUG at fs/btrfs/qgroup.c:365! [ 5.597946] CPU: 1 UID: 0 PID: 268 Comm: mount Not tainted 6.13.0-rc2-00031-gf92f4749861b #146 [ 5.598450] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 [ 5.599008] RIP: 0010:btrfs_read_qgroup_config+0x74d/0x7a0 [ 5.604303] [ 5.605230] ? btrfs_read_qgroup_config+0x74d/0x7a0 [ 5.605538] ? exc_invalid_op+0x56/0x70 [ 5.605775] ? btrfs_read_qgroup_config+0x74d/0x7a0 [ 5.606066] ? asm_exc_invalid_op+0x1f/0x30 [ 5.606441] ? btrfs_read_qgroup_config+0x74d/0x7a0 [ 5.606741] ? btrfs_read_qgroup_config+0x74d/0x7a0 [ 5.607038] ? try_to_wake_up+0x317/0x760 [ 5.607286] open_ctree+0xd9c/0x1710 [ 5.607509] btrfs_get_tree+0x58a/0x7e0 [ 5.608002] vfs_get_tree+0x2e/0x100 [ 5.608224] fc_mount+0x16/0x60 [ 5.608420] btrfs_get_tree+0x2f8/0x7e0 [ 5.608897] vfs_get_tree+0x2e/0x100 [ 5.609121] path_mount+0x4c8/0xbc0 [ 5.609538] __x64_sys_mount+0x10d/0x150 The issue can be easily reproduced using the following reproduer: root@q:linux# cat repro.sh set -e mkfs.btrfs -f /dev/sdb > /dev/null mount /dev/sdb /mnt/btrfs btrfs quota enable -s /mnt/btrfs umount /mnt/btrfs mount /dev/sdb /mnt/btrfs The issue is that when enabling quotas, at btrfs_quota_enable(), we set BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE at fs_info->qgroup_flags and persist it in the quota root in the item with the key BTRFS_QGROUP_STATUS_KEY, but we only set the incompat bit BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA after we commit the transaction used to enable simple quotas. This means that if after that transaction commit we unmount the filesystem without starting and committing any other transaction, or we have a power failure, the next time we mount the filesystem we will find the flag BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE set in the item with the key BTRFS_QGROUP_STATUS_KEY but we will not find the incompat bit BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA set in the superblock, triggering an assertion failure at: btrfs_read_qgroup_config() -> qgroup_read_enable_gen() To fix this issue set the BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA flag immediately after setting the BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE. This ensures that both flags are flushed to disk within the same transaction. Fixes: 182940f4f4db ("btrfs: qgroup: add new quota mode for simple quotas") Reviewed-by: Filipe Manana Signed-off-by: Julian Sun Signed-off-by: Filipe Manana --- fs/btrfs/qgroup.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index c82df56fbf3dcf..993b5e803699ec 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1121,6 +1121,7 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info, fs_info->qgroup_flags = BTRFS_QGROUP_STATUS_FLAG_ON; if (simple) { fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE; + btrfs_set_fs_incompat(fs_info, SIMPLE_QUOTA); btrfs_set_qgroup_status_enable_gen(leaf, ptr, trans->transid); } else { fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT; @@ -1254,8 +1255,6 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info, spin_lock(&fs_info->qgroup_lock); fs_info->quota_root = quota_root; set_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags); - if (simple) - btrfs_set_fs_incompat(fs_info, SIMPLE_QUOTA); spin_unlock(&fs_info->qgroup_lock); /* Skip rescan for simple qgroups. */