From:   Ye Bin <yebin@huaweicloud.com>
To:     djwong@kernel.org, linux-xfs@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, Ye Bin <yebin10@huawei.com>
Subject: [PATCH] xfs: fix possible assert failed in xfs_fs_put_super() when do cpu offline
Date:   Tue, 14 Mar 2023 17:06:49 +0800
Message-Id: <20230314090649.326642-1-yebin@huaweicloud.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Ye Bin <yebin10@huawei.com>

There's a issue when do cpu offline test:
CPU: 48 PID: 1168152 Comm: umount Kdump: loaded Tainted: G L
pstate: 60000005 (nZCv daif -PAN -UAO -TCO BTYPE=--)
pc : assfail+0x8c/0xb4
lr : assfail+0x38/0xb4
sp : ffffa00033ce7c40
x29: ffffa00033ce7c40 x28: ffffa00014794f30
x27: ffffa00014f6ca20 x26: 1fffe0120b2e2030
x25: ffff009059710188 x24: ffff00886c0a4650
x23: 1fffe0110d8148ca x22: ffff009059710180
x21: ffffa00015155680 x20: ffff00886c0a4000
x19: 0000000000000001 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000
x15: 0000000000000007 x14: 1fffe00304cef265
x13: ffff00182642b200 x12: ffff8012d37757bf
x11: 1fffe012d37757be x10: ffff8012d37757be
x9 : ffffa00010603a0c x8 : 0000000041b58ab3
x7 : ffff94000679cf44 x6 : 00000000ffffffc0
x5 : 0000000000000021 x4 : 00000000ffffffca
x3 : 1ffff40002a27ee1 x2 : 0000000000000004
x1 : 0000000000000000 x0 : ffffa0001513f000
Call trace:
 assfail+0x8c/0xb4
 xfs_destroy_percpu_counters+0x98/0xa4
 xfs_fs_put_super+0x1a0/0x2a4
 generic_shutdown_super+0x104/0x2c0
 kill_block_super+0x8c/0xf4
 deactivate_locked_super+0xa4/0x164
 deactivate_super+0xb0/0xdc
 cleanup_mnt+0x29c/0x3ec
 __cleanup_mnt+0x1c/0x30
 task_work_run+0xe0/0x200
 do_notify_resume+0x244/0x320
 work_pending+0xc/0xa0

We analyzed the data in vmcore is correct. But triggered above issue.
As f689054aace2 ("percpu_counter: add percpu_counter_sum_all interface")
commit describes there is a small race window between the online CPUs traversal
of percpu_counter_sum and the CPU offline callback. This means percpu_counter_sum()
may return incorrect result during cpu offline.
To solve above issue use percpu_counter_sum_all() interface to make sure
result is correct to prevent false triggering of assertions.

Signed-off-by: Ye Bin <yebin10@huawei.com>
---
 fs/xfs/xfs_super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 2479b5cbd75e..c0ce66f966ee 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1076,7 +1076,7 @@ xfs_destroy_percpu_counters(
 	percpu_counter_destroy(&mp->m_ifree);
 	percpu_counter_destroy(&mp->m_fdblocks);
 	ASSERT(xfs_is_shutdown(mp) ||
-	       percpu_counter_sum(&mp->m_delalloc_blks) == 0);
+	       percpu_counter_sum_all(&mp->m_delalloc_blks) == 0);
 	percpu_counter_destroy(&mp->m_delalloc_blks);
 	percpu_counter_destroy(&mp->m_frextents);
 }
-- 
2.31.1