linux-kernel - [PATCH] btrfs: fix an assertion failure related to squota feature.

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Message-Id: <20241211111315.65007-1-sunjunchao2870@gmail.com>
Date: Wed, 11 Dec 2024 19:13:15 +0800
From: Julian Sun <sunjunchao2870@...il.com>
To: linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: clm@...com,
	josef@...icpanda.com,
	dsterba@...e.com,
	wqu@...e.com,
	Julian Sun <sunjunchao2870@...il.com>
Subject: [PATCH] btrfs: fix an assertion failure related to squota 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]  <TASK>
[    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 root cause of this issue is as follows:
When simple quota is enabled, the BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA
flag is set after btrfs_commit_transaction(), whereas the
BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE flag is set before btrfs_commit_transaction(),
which led to the first flag not being flushed to disk, and the second
flag is successfully flushed. Finally causes this assertion failure
after umount && mount again.

To resolve this issue, the BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA flag
is set immediately after setting the BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE.
This ensures that both flags are flushed to disk within the same
transaction.

Signed-off-by: Julian Sun <sunjunchao2870@...il.com>
---
 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 a6f92836c9b1..f9b214992212 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. */
-- 
2.39.5