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Mon, 23 Jun 2025 03:10:21 +0200 Message-ID: <6d867d2b-cbfd-41ae-b8bb-d12415119974@gmx.com> Date: Mon, 23 Jun 2025 10:40:18 +0930 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 0/6] btrfs: use the super_block as bdev holder To: dsterba@suse.cz, Qu Wenruo Cc: linux-btrfs@vger.kernel.org References: <20250619132918.GK4037@twin.jikos.cz> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNIlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT7CwJQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCZxF1YAUJEP5a sQAKCRDCPZHzoSX+qF+mB/9gXu9C3BV0omDZBDWevJHxpWpOwQ8DxZEbk9b9LcrQlWdhFhyn xi+l5lRziV9ZGyYXp7N35a9t7GQJndMCFUWYoEa+1NCuxDs6bslfrCaGEGG/+wd6oIPb85xo naxnQ+SQtYLUFbU77WkUPaaIU8hH2BAfn9ZSDX9lIxheQE8ZYGGmo4wYpnN7/hSXALD7+oun tZljjGNT1o+/B8WVZtw/YZuCuHgZeaFdhcV2jsz7+iGb+LsqzHuznrXqbyUQgQT9kn8ZYFNW 7tf+LNxXuwedzRag4fxtR+5GVvJ41Oh/eygp8VqiMAtnFYaSlb9sjia1Mh+m+OBFeuXjgGlG VvQFzsBNBFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcga CbPEwhLj1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj /IrRUUka68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fN GSsRb+pKEKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0 q1eW4Jrv0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEv ABEBAAHCwHwEGAEIACYCGwwWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCZxF1gQUJEP5a0gAK CRDCPZHzoSX+qHGpB/kB8A7M7KGL5qzat+jBRoLwB0Y3Zax0QWuANVdZM3eJDlKJKJ4HKzjo B2Pcn4JXL2apSan2uJftaMbNQbwotvabLXkE7cPpnppnBq7iovmBw++/d8zQjLQLWInQ5kNq Vmi36kmq8o5c0f97QVjMryHlmSlEZ2Wwc1kURAe4lsRG2dNeAd4CAqmTw0cMIrR6R/Dpt3ma +8oGXJOmwWuDFKNV4G2XLKcghqrtcRf2zAGNogg3KulCykHHripG3kPKsb7fYVcSQtlt5R6v HZStaZBzw4PcDiaAF3pPDBd+0fIKS6BlpeNRSFG94RYrt84Qw77JWDOAZsyNfEIEE0J6LSR/ In-Reply-To: <20250619132918.GK4037@twin.jikos.cz> Content-Type: text/plain; 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The problem is exactly in the btrfs_open_devices() handling. The new delayed behavior is causing lockdep warning, as now sget_fc() is= =20 called with uuid_mutex hold, this can cause a ABBA deadlock: [ 50.807904] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D [ 50.809738] WARNING: possible circular locking dependency detected [ 50.811563] 6.16.0-rc1-custom+ #258 Not tainted [ 50.813040] ------------------------------------------------------ [ 50.814761] mount/798 is trying to acquire lock: [ 50.816114] ffffffffa070b068 (uuid_mutex){+.+.}-{4:4}, at:=20 btrfs_read_chunk_tree+0x7d/0x870 [btrfs] [ 50.818690] [ 50.818690] but task is already holding lock: [ 50.820964] ffff8881055d50e0 (&type->s_umount_key#46/1){+.+.}-{4:4},=20 at: alloc_super+0xe0/0x3c0 [ 50.823553] [ 50.823553] which lock already depends on the new lock. [ 50.823553] [ 50.825852] [ 50.825852] the existing dependency chain (in reverse order) is: [ 50.827858] [ 50.827858] -> #1 (&type->s_umount_key#46/1){+.+.}-{4:4}: [ 50.829749] down_write_nested+0x38/0xc0 [ 50.831063] alloc_super+0xe0/0x3c0 [ 50.832175] sget_fc+0x66/0x400 [ 50.833203] btrfs_get_tree+0x195/0x620 [btrfs] [ 50.834653] vfs_get_tree+0x2c/0xe0 [ 50.835767] vfs_cmd_create+0x57/0xd0 [ 50.836979] __do_sys_fsconfig+0x4c0/0x660 [ 50.838244] do_syscall_64+0x6c/0x2c0 [ 50.839397] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 50.840968] [ 50.840968] -> #0 (uuid_mutex){+.+.}-{4:4}: [ 50.842767] __lock_acquire+0x14b7/0x22a0 [ 50.844138] lock_acquire+0xc9/0x300 [ 50.845427] __mutex_lock+0xb9/0xe00 [ 50.846625] btrfs_read_chunk_tree+0x7d/0x870 [btrfs] [ 50.848272] open_ctree+0x9aa/0x1483 [btrfs] [ 50.849654] btrfs_get_tree.cold+0xf3/0x19d [btrfs] [ 50.851173] vfs_get_tree+0x2c/0xe0 [ 50.852443] vfs_cmd_create+0x57/0xd0 [ 50.853768] __do_sys_fsconfig+0x4c0/0x660 [ 50.855094] do_syscall_64+0x6c/0x2c0 [ 50.856260] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 50.857773] [ 50.857773] other info that might help us debug this: [ 50.857773] [ 50.859955] Possible unsafe locking scenario: [ 50.859955] [ 50.861558] CPU0 CPU1 [ 50.862816] ---- ---- [ 50.864067] lock(&type->s_umount_key#46/1); [ 50.865367] lock(uuid_mutex); [ 50.866962]=20 lock(&type->s_umount_key#46/1); [ 50.868821] lock(uuid_mutex); [ 50.869716] [ 50.869716] *** DEADLOCK *** [ 50.869716] [ 50.871325] 2 locks held by mount/798: [ 50.872370] #0: ffff888102ea2c70 (&fc->uapi_mutex){+.+.}-{4:4}, at:=20 __do_sys_fsconfig+0x48f/0x660 [ 50.874799] #1: ffff8881055d50e0=20 (&type->s_umount_key#46/1){+.+.}-{4:4}, at: alloc_super+0xe0/0x3c0 [ 50.877270] [ 50.877270] stack backtrace: [ 50.878480] CPU: 3 UID: 0 PID: 798 Comm: mount Not tainted=20 6.16.0-rc1-custom+ #258 PREEMPT(full) [ 50.878486] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS=20 unknown 02/02/2022 [ 50.878488] Call Trace: [ 50.878493] [ 50.878498] dump_stack_lvl+0x76/0xa0 [ 50.878505] print_circular_bug.cold+0x185/0x1d0 [ 50.878512] check_noncircular+0x169/0x190 [ 50.878518] __lock_acquire+0x14b7/0x22a0 [ 50.878526] lock_acquire+0xc9/0x300 [ 50.878529] ? btrfs_read_chunk_tree+0x7d/0x870 [btrfs] [ 50.878626] ? lock_acquire+0xc9/0x300 [ 50.878628] ? fs_reclaim_acquire+0x4f/0xe0 [ 50.878634] __mutex_lock+0xb9/0xe00 [ 50.878640] ? btrfs_read_chunk_tree+0x7d/0x870 [btrfs] [ 50.878685] ? fs_reclaim_acquire+0x4f/0xe0 [ 50.878687] ? lock_release+0xdd/0x2e0 [ 50.878690] ? btrfs_read_chunk_tree+0x7d/0x870 [btrfs] [ 50.878726] ? btrfs_read_chunk_tree+0x7d/0x870 [btrfs] [ 50.878759] btrfs_read_chunk_tree+0x7d/0x870 [btrfs] [ 50.878793] ? btrfs_root_node+0x22/0x220 [btrfs] [ 50.878844] ? find_held_lock+0x2b/0x80 [ 50.878849] ? btrfs_root_node+0x9c/0x220 [btrfs] [ 50.878912] ? load_super_root+0x95/0xc3 [btrfs] [ 50.878976] open_ctree+0x9aa/0x1483 [btrfs] [ 50.879015] btrfs_get_tree.cold+0xf3/0x19d [btrfs] [ 50.879053] ? fscontext_read+0x11d/0x130 [ 50.879056] ? __do_sys_fsconfig+0x48f/0x660 [ 50.879058] vfs_get_tree+0x2c/0xe0 [ 50.879062] ? capable+0x3a/0x60 [ 50.879066] vfs_cmd_create+0x57/0xd0 [ 50.879069] __do_sys_fsconfig+0x4c0/0x660 [ 50.879071] do_syscall_64+0x6c/0x2c0 [ 50.879077] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 50.879080] RIP: 0033:0x7f3442f9eefe [ 50.879086] Code: 73 01 c3 48 8b 0d 12 be 0c 00 f7 d8 64 89 01 48 83=20 c8 ff c3 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 49 89 ca b8 af 01 00 00 0f=20 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d e2 bd 0c 00 f7 d8 64 89 01 48 [ 50.879088] RSP: 002b:00007ffe661382a8 EFLAGS: 00000246 ORIG_RAX:=20 00000000000001af [ 50.879092] RAX: ffffffffffffffda RBX: 0000558220e95430 RCX:=20 00007f3442f9eefe [ 50.879094] RDX: 0000000000000000 RSI: 0000000000000006 RDI:=20 0000000000000003 [ 50.879094] RBP: 00007ffe661382e0 R08: 0000000000000000 R09:=20 0000000000000000 [ 50.879095] R10: 0000000000000000 R11: 0000000000000246 R12:=20 00007f34430c8980 [ 50.879096] R13: 0000000000000000 R14: 0000558220e96720 R15:=20 00007f34430bd8e0 [ 50.879099] I'll need to find out a way to make sget_fc() call without holding=20 uuid_mutex instead. Thanks, Qu