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[2003:d8:2f05:e100:526f:9b8:bd2a:2997]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fb8811ae8sm17058049f8f.19.2025.09.29.01.22.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Sep 2025 01:22:55 -0700 (PDT) Message-ID: <6b473885-cb16-4b57-b863-bcba22083c12@redhat.com> Date: Mon, 29 Sep 2025 10:22:53 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] possible deadlock in ksm_do_scan To: syzbot , akpm@linux-foundation.org, chengming.zhou@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, xu.xin16@zte.com.cn References: <68d95f20.a70a0220.10c4b.0022.GAE@google.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ 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3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <68d95f20.a70a0220.10c4b.0022.GAE@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 28.09.25 18:15, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: b5a4da2c459f Add linux-next specific files for 20250924 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=15a154e2580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=841973c5ab4f4157 > dashboard link: https://syzkaller.appspot.com/bug?extid=f1b91395f2bcbcc8128b > compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/2d0e39514585/disk-b5a4da2c.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/c7c8001fe2ea/vmlinux-b5a4da2c.xz > kernel image: https://storage.googleapis.com/syzbot-assets/807bea872f12/bzImage-b5a4da2c.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+f1b91395f2bcbcc8128b@syzkaller.appspotmail.com > > ====================================================== > WARNING: possible circular locking dependency detected > syzkaller #0 Not tainted > ------------------------------------------------------ > ksmd/37 is trying to acquire lock: > ffffffff8e645220 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:318 [inline] > ffffffff8e645220 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4896 [inline] > ffffffff8e645220 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:5220 [inline] > ffffffff8e645220 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_noprof+0x45/0x6e0 mm/slub.c:5251 > > but task is already holding lock: > ffff888028ba01e0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock include/linux/mmap_lock.h:368 [inline] > ffff888028ba01e0 (&mm->mmap_lock){++++}-{4:4}, at: scan_get_next_rmap_item mm/ksm.c:2532 [inline] > ffff888028ba01e0 (&mm->mmap_lock){++++}-{4:4}, at: ksm_do_scan+0x602/0x6540 mm/ksm.c:2659 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #7 (&mm->mmap_lock){++++}-{4:4}: > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > __might_fault+0xcc/0x130 mm/memory.c:7125 > _copy_from_iter+0xf3/0x1790 lib/iov_iter.c:259 > copy_from_iter include/linux/uio.h:228 [inline] > copy_from_iter_full include/linux/uio.h:245 [inline] > skb_do_copy_data_nocache include/net/sock.h:2269 [inline] > skb_copy_to_page_nocache include/net/sock.h:2295 [inline] > tcp_sendmsg_locked+0x2347/0x5540 net/ipv4/tcp.c:1272 > tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1413 > sock_sendmsg_nosec net/socket.c:714 [inline] > __sock_sendmsg+0x19c/0x270 net/socket.c:729 > sock_write_iter+0x279/0x360 net/socket.c:1182 > new_sync_write fs/read_write.c:593 [inline] > vfs_write+0x5c9/0xb30 fs/read_write.c:686 > ksys_write+0x145/0x250 fs/read_write.c:738 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > -> #6 (sk_lock-AF_INET){+.+.}-{0:0}: > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > lock_sock_nested+0x48/0x100 net/core/sock.c:3720 > lock_sock include/net/sock.h:1679 [inline] > inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:907 > nbd_mark_nsock_dead+0x2e9/0x560 drivers/block/nbd.c:318 > sock_shutdown+0x15e/0x260 drivers/block/nbd.c:411 > nbd_clear_sock drivers/block/nbd.c:1424 [inline] > nbd_config_put+0x342/0x790 drivers/block/nbd.c:1448 > nbd_release+0xfe/0x140 drivers/block/nbd.c:1753 > bdev_release+0x536/0x650 block/bdev.c:-1 > blkdev_release+0x15/0x20 block/fops.c:702 > __fput+0x44c/0xa70 fs/file_table.c:468 > task_work_run+0x1d4/0x260 kernel/task_work.c:227 > resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] > exit_to_user_mode_loop+0xe9/0x130 kernel/entry/common.c:43 > exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline] > syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline] > syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline] > do_syscall_64+0x2bd/0xfa0 arch/x86/entry/syscall_64.c:100 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > -> #5 (&nsock->tx_lock){+.+.}-{4:4}: > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > __mutex_lock_common kernel/locking/mutex.c:598 [inline] > __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760 > nbd_handle_cmd drivers/block/nbd.c:1140 [inline] > nbd_queue_rq+0x257/0xf10 drivers/block/nbd.c:1204 > blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2129 > __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline] > blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline] > __blk_mq_sched_dispatch_requests+0xda4/0x1570 block/blk-mq-sched.c:307 > blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 > blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2367 > blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1 > blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2976 > __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1225 > blk_finish_plug block/blk-core.c:1252 [inline] > __submit_bio+0x2d3/0x5a0 block/blk-core.c:651 > __submit_bio_noacct_mq block/blk-core.c:724 [inline] > submit_bio_noacct_nocheck+0x2fb/0xa50 block/blk-core.c:755 > submit_bh fs/buffer.c:2829 [inline] > block_read_full_folio+0x599/0x830 fs/buffer.c:2447 > filemap_read_folio+0x117/0x380 mm/filemap.c:2444 > do_read_cache_folio+0x350/0x590 mm/filemap.c:4009 > read_mapping_folio include/linux/pagemap.h:999 [inline] > read_part_sector+0xb6/0x2b0 block/partitions/core.c:722 > adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360 > check_partition block/partitions/core.c:141 [inline] > blk_add_partitions block/partitions/core.c:589 [inline] > bdev_disk_changed+0x75f/0x14b0 block/partitions/core.c:693 > blkdev_get_whole+0x380/0x510 block/bdev.c:748 > bdev_open+0x31e/0xd30 block/bdev.c:957 > blkdev_open+0x457/0x600 block/fops.c:694 > do_dentry_open+0x953/0x13f0 fs/open.c:965 > vfs_open+0x3b/0x340 fs/open.c:1097 > do_open fs/namei.c:3975 [inline] > path_openat+0x2ee5/0x3830 fs/namei.c:4134 > do_filp_open+0x1fa/0x410 fs/namei.c:4161 > do_sys_openat2+0x121/0x1c0 fs/open.c:1437 > do_sys_open fs/open.c:1452 [inline] > __do_sys_openat fs/open.c:1468 [inline] > __se_sys_openat fs/open.c:1463 [inline] > __x64_sys_openat+0x138/0x170 fs/open.c:1463 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > -> #4 (&cmd->lock){+.+.}-{4:4}: > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > __mutex_lock_common kernel/locking/mutex.c:598 [inline] > __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760 > nbd_queue_rq+0xc8/0xf10 drivers/block/nbd.c:1196 > blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2129 > __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline] > blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline] > __blk_mq_sched_dispatch_requests+0xda4/0x1570 block/blk-mq-sched.c:307 > blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 > blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2367 > blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1 > blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2976 > __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1225 > blk_finish_plug block/blk-core.c:1252 [inline] > __submit_bio+0x2d3/0x5a0 block/blk-core.c:651 > __submit_bio_noacct_mq block/blk-core.c:724 [inline] > submit_bio_noacct_nocheck+0x2fb/0xa50 block/blk-core.c:755 > submit_bh fs/buffer.c:2829 [inline] > block_read_full_folio+0x599/0x830 fs/buffer.c:2447 > filemap_read_folio+0x117/0x380 mm/filemap.c:2444 > do_read_cache_folio+0x350/0x590 mm/filemap.c:4009 > read_mapping_folio include/linux/pagemap.h:999 [inline] > read_part_sector+0xb6/0x2b0 block/partitions/core.c:722 > adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360 > check_partition block/partitions/core.c:141 [inline] > blk_add_partitions block/partitions/core.c:589 [inline] > bdev_disk_changed+0x75f/0x14b0 block/partitions/core.c:693 > blkdev_get_whole+0x380/0x510 block/bdev.c:748 > bdev_open+0x31e/0xd30 block/bdev.c:957 > blkdev_open+0x457/0x600 block/fops.c:694 > do_dentry_open+0x953/0x13f0 fs/open.c:965 > vfs_open+0x3b/0x340 fs/open.c:1097 > do_open fs/namei.c:3975 [inline] > path_openat+0x2ee5/0x3830 fs/namei.c:4134 > do_filp_open+0x1fa/0x410 fs/namei.c:4161 > do_sys_openat2+0x121/0x1c0 fs/open.c:1437 > do_sys_open fs/open.c:1452 [inline] > __do_sys_openat fs/open.c:1468 [inline] > __se_sys_openat fs/open.c:1463 [inline] > __x64_sys_openat+0x138/0x170 fs/open.c:1463 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > -> #3 (set->srcu){.+.+}-{0:0}: > lock_sync+0xba/0x160 kernel/locking/lockdep.c:5916 > srcu_lock_sync include/linux/srcu.h:173 [inline] > __synchronize_srcu+0x96/0x3a0 kernel/rcu/srcutree.c:1429 > elevator_switch+0x12b/0x640 block/elevator.c:588 > elevator_change+0x315/0x4c0 block/elevator.c:691 > elevator_set_default+0x186/0x260 block/elevator.c:767 > blk_register_queue+0x34e/0x3f0 block/blk-sysfs.c:942 > __add_disk+0x677/0xd50 block/genhd.c:528 > add_disk_fwnode+0xfc/0x480 block/genhd.c:597 > add_disk include/linux/blkdev.h:775 [inline] > nbd_dev_add+0x717/0xae0 drivers/block/nbd.c:1981 > nbd_init+0x168/0x1f0 drivers/block/nbd.c:2688 > do_one_initcall+0x236/0x820 init/main.c:1283 > do_initcall_level+0x104/0x190 init/main.c:1345 > do_initcalls+0x59/0xa0 init/main.c:1361 > kernel_init_freeable+0x334/0x4b0 init/main.c:1593 > kernel_init+0x1d/0x1d0 init/main.c:1483 > ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > -> #2 (&q->elevator_lock){+.+.}-{4:4}: > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > __mutex_lock_common kernel/locking/mutex.c:598 [inline] > __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760 > elevator_change+0x1e5/0x4c0 block/elevator.c:689 > elevator_set_none+0x42/0xb0 block/elevator.c:782 > blk_mq_elv_switch_none block/blk-mq.c:5032 [inline] > __blk_mq_update_nr_hw_queues block/blk-mq.c:5075 [inline] > blk_mq_update_nr_hw_queues+0x598/0x1ab0 block/blk-mq.c:5133 > nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1486 > nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2236 > genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115 > genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] > genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210 > netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552 > genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 > netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] > netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346 > netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896 > sock_sendmsg_nosec net/socket.c:714 [inline] > __sock_sendmsg+0x21c/0x270 net/socket.c:729 > ____sys_sendmsg+0x505/0x830 net/socket.c:2617 > ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2671 > __sys_sendmsg net/socket.c:2703 [inline] > __do_sys_sendmsg net/socket.c:2708 [inline] > __se_sys_sendmsg net/socket.c:2706 [inline] > __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2706 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > -> #1 (&q->q_usage_counter(io)#49){++++}-{0:0}: > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > blk_alloc_queue+0x538/0x620 block/blk-core.c:461 > blk_mq_alloc_queue block/blk-mq.c:4399 [inline] > __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4446 > nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1951 > nbd_init+0x168/0x1f0 drivers/block/nbd.c:2688 > do_one_initcall+0x236/0x820 init/main.c:1283 > do_initcall_level+0x104/0x190 init/main.c:1345 > do_initcalls+0x59/0xa0 init/main.c:1361 > kernel_init_freeable+0x334/0x4b0 init/main.c:1593 > kernel_init+0x1d/0x1d0 init/main.c:1483 > ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > -> #0 (fs_reclaim){+.+.}-{0:0}: > check_prev_add kernel/locking/lockdep.c:3165 [inline] > check_prevs_add kernel/locking/lockdep.c:3284 [inline] > validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 > __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > __fs_reclaim_acquire mm/page_alloc.c:4269 [inline] > fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4283 > might_alloc include/linux/sched/mm.h:318 [inline] > slab_pre_alloc_hook mm/slub.c:4896 [inline] > slab_alloc_node mm/slub.c:5220 [inline] > kmem_cache_alloc_noprof+0x45/0x6e0 mm/slub.c:5251 > alloc_rmap_item mm/ksm.c:565 [inline] > get_next_rmap_item mm/ksm.c:2378 [inline] > scan_get_next_rmap_item mm/ksm.c:2565 [inline] > ksm_do_scan+0xbaf/0x6540 mm/ksm.c:2659 > ksm_scan_thread+0x10b/0x4b0 mm/ksm.c:2684 > kthread+0x711/0x8a0 kernel/kthread.c:463 > ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > other info that might help us debug this: > > Chain exists of: > fs_reclaim --> sk_lock-AF_INET --> &mm->mmap_lock > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > rlock(&mm->mmap_lock); > lock(sk_lock-AF_INET); > lock(&mm->mmap_lock); > lock(fs_reclaim); KSM simply holds the mmap lock here while performing an allocation that might trigger reclaim. Nothing special about that. So the issue (if true) is likely somewhere in the sk_lock-AF_INET path. -- Cheers David / dhildenb