From: Qu Wenruo wqu@suse.com
commit 75181406b4eafacc531ff2ee5fb032bd93317e2b upstream.
[BUG] There are some reports from the mailing list that since v6.1 kernel, the WARN_ON() inside btrfs_qgroup_account_extent() gets triggered during rescan:
WARNING: CPU: 3 PID: 6424 at fs/btrfs/qgroup.c:2756 btrfs_qgroup_account_extents+0x1ae/0x260 [btrfs] CPU: 3 PID: 6424 Comm: snapperd Tainted: P OE 6.1.2-1-default #1 openSUSE Tumbleweed 05c7a1b1b61d5627475528f71f50444637b5aad7 RIP: 0010:btrfs_qgroup_account_extents+0x1ae/0x260 [btrfs] Call Trace: <TASK> btrfs_commit_transaction+0x30c/0xb40 [btrfs c39c9c546c241c593f03bd6d5f39ea1b676250f6] ? start_transaction+0xc3/0x5b0 [btrfs c39c9c546c241c593f03bd6d5f39ea1b676250f6] btrfs_qgroup_rescan+0x42/0xc0 [btrfs c39c9c546c241c593f03bd6d5f39ea1b676250f6] btrfs_ioctl+0x1ab9/0x25c0 [btrfs c39c9c546c241c593f03bd6d5f39ea1b676250f6] ? __rseq_handle_notify_resume+0xa9/0x4a0 ? mntput_no_expire+0x4a/0x240 ? __seccomp_filter+0x319/0x4d0 __x64_sys_ioctl+0x90/0xd0 do_syscall_64+0x5b/0x80 ? syscall_exit_to_user_mode+0x17/0x40 ? do_syscall_64+0x67/0x80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7fd9b790d9bf </TASK>
[CAUSE] Since commit e15e9f43c7ca ("btrfs: introduce BTRFS_QGROUP_RUNTIME_FLAG_NO_ACCOUNTING to skip qgroup accounting"), if our qgroup is already in inconsistent state, we will no longer do the time-consuming backref walk.
This can leave some qgroup records without a valid old_roots ulist. Normally this is fine, as btrfs_qgroup_account_extents() would also skip those records if we have NO_ACCOUNTING flag set.
But there is a small window, if we have NO_ACCOUNTING flag set, and inserted some qgroup_record without a old_roots ulist, but then the user triggered a qgroup rescan.
During btrfs_qgroup_rescan(), we firstly clear NO_ACCOUNTING flag, then commit current transaction.
And since we have a qgroup_record with old_roots = NULL, we trigger the WARN_ON() during btrfs_qgroup_account_extents().
[FIX] Unfortunately due to the introduction of NO_ACCOUNTING flag, the assumption that every qgroup_record would have its old_roots populated is no longer correct.
Fix the false alerts and drop the WARN_ON().
Reported-by: Lukas Straub lukasstraub2@web.de Reported-by: HanatoK summersnow9403@gmail.com Fixes: e15e9f43c7ca ("btrfs: introduce BTRFS_QGROUP_RUNTIME_FLAG_NO_ACCOUNTING to skip qgroup accounting") CC: stable@vger.kernel.org # 6.1 Link: https://lore.kernel.org/linux-btrfs/2403c697-ddaf-58ad-3829-0335fc89df09@gma... Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/qgroup.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
--- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -2751,9 +2751,19 @@ int btrfs_qgroup_account_extents(struct BTRFS_QGROUP_RUNTIME_FLAG_NO_ACCOUNTING)) { /* * Old roots should be searched when inserting qgroup - * extent record + * extent record. + * + * But for INCONSISTENT (NO_ACCOUNTING) -> rescan case, + * we may have some record inserted during + * NO_ACCOUNTING (thus no old_roots populated), but + * later we start rescan, which clears NO_ACCOUNTING, + * leaving some inserted records without old_roots + * populated. + * + * Those cases are rare and should not cause too much + * time spent during commit_transaction(). */ - if (WARN_ON(!record->old_roots)) { + if (!record->old_roots) { /* Search commit root to find old_roots */ ret = btrfs_find_all_roots(NULL, fs_info, record->bytenr, 0,