[syzbot] [mm?] possible deadlock in gup_fast_fallback (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 63751099502d Merge branch 'net-mlx5-steering-misc-enhancem..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1714fbce580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f2b487b72ffad035
dashboard link: https://syzkaller.appspot.com/bug?extid=8edc46c9c781c802acf4
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1f8de738e2f8/disk-63751099.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ae6cfb0d3b70/vmlinux-63751099.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f00e218e1a55/bzImage-63751099.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8edc46...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.2801/16593 is trying to acquire lock:
ffff88802ae527f8 (&mm->mmap_lock){++++}-{4:4}, at: gup_fast_fallback+0x20d/0x20d0 mm/gup.c:3193

but task is already holding lock:
ffff888055ac9d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
ffff888055ac9d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: tls_sw_sendmsg+0x15d/0x2430 net/tls/tls_sw.c:1291

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (sk_lock-AF_INET6){+.+.}-{0:0}:
lock_sock_nested+0x41/0x100 net/core/sock.c:3783
lock_sock include/net/sock.h:1713 [inline]
inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:915
nbd_mark_nsock_dead+0x2e9/0x560 drivers/block/nbd.c:318
sock_shutdown+0x15e/0x260 drivers/block/nbd.c:411
nbd_clear_sock+0x24/0x170 drivers/block/nbd.c:1427
nbd_config_put+0x2dd/0x580 drivers/block/nbd.c:1451
nbd_genl_connect+0x19d5/0x1cf0 drivers/block/nbd.c:2248
genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2551
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x75c/0x8e0 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1895
sock_sendmsg_nosec net/socket.c:787 [inline]
__sock_sendmsg net/socket.c:802 [inline]
____sys_sendmsg+0x972/0x9f0 net/socket.c:2698
___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
__sys_sendmsg net/socket.c:2784 [inline]
__do_sys_sendmsg net/socket.c:2789 [inline]
__se_sys_sendmsg net/socket.c:2787 [inline]
__x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a3/0x1550 kernel/locking/mutex.c:820
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x37b/0x1100 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0xa70/0x1910 block/blk-mq.c:2148
__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+0xdcc/0x1600 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:2386
blk_mq_dispatch_list+0xd16/0xe10 include/linux/spinlock.h:-1
blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
__blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x28d/0x580 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:753
submit_bh fs/buffer.c:2742 [inline]
block_read_full_folio+0x599/0x830 fs/buffer.c:2344
filemap_read_folio+0x137/0x3b0 mm/filemap.c:2502
do_read_cache_folio+0x358/0x590 mm/filemap.c:4107
read_mapping_folio include/linux/pagemap.h:1017 [inline]
read_part_sector+0xb6/0x2b0 block/partitions/core.c:724
adfspart_check_ICS+0xb1/0x960 block/partitions/acorn.c:356
check_partition block/partitions/core.c:143 [inline]
blk_add_partitions block/partitions/core.c:591 [inline]
bdev_disk_changed+0x817/0x1770 block/partitions/core.c:695
blkdev_get_whole+0x380/0x510 block/bdev.c:756
bdev_open+0x31e/0xd30 block/bdev.c:965
blkdev_open+0x470/0x610 block/fops.c:697
do_dentry_open+0x785/0x14e0 fs/open.c:947
vfs_open+0x3b/0x340 fs/open.c:1079
do_open fs/namei.c:4699 [inline]
path_openat+0x2e08/0x3860 fs/namei.c:4858
do_file_open+0x23e/0x4a0 fs/namei.c:4887
do_sys_openat2+0x113/0x200 fs/open.c:1364
do_sys_open fs/open.c:1370 [inline]
__do_sys_openat fs/open.c:1386 [inline]
__se_sys_openat fs/open.c:1381 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1381
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (&cmd->lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a3/0x1550 kernel/locking/mutex.c:820
nbd_queue_rq+0xc6/0x1100 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0xa70/0x1910 block/blk-mq.c:2148
__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+0xdcc/0x1600 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:2386
blk_mq_dispatch_list+0xd16/0xe10 include/linux/spinlock.h:-1
blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
__blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x28d/0x580 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:753
submit_bh fs/buffer.c:2742 [inline]
block_read_full_folio+0x599/0x830 fs/buffer.c:2344
filemap_read_folio+0x137/0x3b0 mm/filemap.c:2502
do_read_cache_folio+0x358/0x590 mm/filemap.c:4107
read_mapping_folio include/linux/pagemap.h:1017 [inline]
read_part_sector+0xb6/0x2b0 block/partitions/core.c:724
adfspart_check_ICS+0xb1/0x960 block/partitions/acorn.c:356
check_partition block/partitions/core.c:143 [inline]
blk_add_partitions block/partitions/core.c:591 [inline]
bdev_disk_changed+0x817/0x1770 block/partitions/core.c:695
blkdev_get_whole+0x380/0x510 block/bdev.c:756
bdev_open+0x31e/0xd30 block/bdev.c:965
blkdev_open+0x470/0x610 block/fops.c:697
do_dentry_open+0x785/0x14e0 fs/open.c:947
vfs_open+0x3b/0x340 fs/open.c:1079
do_open fs/namei.c:4699 [inline]
path_openat+0x2e08/0x3860 fs/namei.c:4858
do_file_open+0x23e/0x4a0 fs/namei.c:4887
do_sys_openat2+0x113/0x200 fs/open.c:1364
do_sys_open fs/open.c:1370 [inline]
__do_sys_openat fs/open.c:1386 [inline]
__se_sys_openat fs/open.c:1381 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1381
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (set->srcu){.+.+}-{0:0}:
srcu_lock_sync include/linux/srcu.h:199 [inline]
__synchronize_srcu+0xca/0x300 kernel/rcu/srcutree.c:1481
elevator_switch+0x1e8/0x7a0 block/elevator.c:576
elevator_change+0x2cc/0x450 block/elevator.c:681
elevator_set_default+0x36c/0x430 block/elevator.c:754
blk_register_queue+0x3e9/0x4e0 block/blk-sysfs.c:987
__add_disk+0x677/0xd50 block/genhd.c:528
add_disk_fwnode+0xfb/0x480 block/genhd.c:597
add_disk include/linux/blkdev.h:794 [inline]
nbd_dev_add+0x72c/0xb50 drivers/block/nbd.c:1984
nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
do_one_initcall+0x250/0x870 init/main.c:1392
do_initcall_level+0x104/0x190 init/main.c:1454
do_initcalls+0x59/0xa0 init/main.c:1470
kernel_init_freeable+0x2a6/0x3e0 init/main.c:1703
kernel_init+0x1d/0x1d0 init/main.c:1593
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (&q->elevator_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a3/0x1550 kernel/locking/mutex.c:820
elevator_change+0x1b3/0x450 block/elevator.c:679
elevator_set_none+0xb5/0x140 block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5131 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5176 [inline]
blk_mq_update_nr_hw_queues+0x5e7/0x1a60 block/blk-mq.c:5241
nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1489
nbd_genl_connect+0x165b/0x1cf0 drivers/block/nbd.c:2239
genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2551
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x75c/0x8e0 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1895
sock_sendmsg_nosec net/socket.c:787 [inline]
__sock_sendmsg net/socket.c:802 [inline]
____sys_sendmsg+0x972/0x9f0 net/socket.c:2698
___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
__sys_sendmsg net/socket.c:2784 [inline]
__do_sys_sendmsg net/socket.c:2789 [inline]
__se_sys_sendmsg net/socket.c:2787 [inline]
__x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&q->q_usage_counter(io)#49){++++}-{0:0}:
blk_alloc_queue+0x546/0x680 block/blk-core.c:461
blk_mq_alloc_queue block/blk-mq.c:4450 [inline]
__blk_mq_alloc_disk+0x197/0x390 block/blk-mq.c:4497
nbd_dev_add+0x499/0xb50 drivers/block/nbd.c:1954
nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
do_one_initcall+0x250/0x870 init/main.c:1392
do_initcall_level+0x104/0x190 init/main.c:1454
do_initcalls+0x59/0xa0 init/main.c:1470
kernel_init_freeable+0x2a6/0x3e0 init/main.c:1703
kernel_init+0x1d/0x1d0 init/main.c:1593
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire mm/page_alloc.c:4325 [inline]
fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4339
might_alloc include/linux/sched/mm.h:317 [inline]
slab_pre_alloc_hook mm/slub.c:4520 [inline]
slab_alloc_node mm/slub.c:4875 [inline]
kmem_cache_alloc_noprof+0x40/0x650 mm/slub.c:4905
mt_alloc_one lib/maple_tree.c:139 [inline]
mas_alloc_nodes+0x291/0x350 lib/maple_tree.c:1089
mas_preallocate+0x2d6/0x640 lib/maple_tree.c:4961
vma_iter_prealloc mm/vma.h:577 [inline]
vma_link+0x123/0x470 mm/vma.c:1849
insert_vm_struct+0x1a5/0x270 mm/vma.c:3325
create_init_stack_vma+0x546/0x9b0 mm/vma_exec.c:147
bprm_mm_init fs/exec.c:274 [inline]
alloc_bprm+0x495/0x5c0 fs/exec.c:1457
class_bprm_constructor fs/exec.c:1466 [inline]
kernel_execve+0x87/0x930 fs/exec.c:1859
try_to_run_init_process+0x13/0x60 init/main.c:1521
kernel_init+0xad/0x1d0 init/main.c:1649
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&mm->mmap_lock){++++}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
gup_fast_fallback+0x226/0x20d0 mm/gup.c:3193
__iov_iter_get_pages_alloc+0x370/0xa10 lib/iov_iter.c:1091
iov_iter_get_pages2+0x5e/0xa0 lib/iov_iter.c:1137
sk_msg_zerocopy_from_iter+0x22c/0x880 net/core/skmsg.c:328
tls_sw_sendmsg_locked net/tls/tls_sw.c:1140 [inline]
tls_sw_sendmsg+0x9f5/0x2430 net/tls/tls_sw.c:1292
sock_sendmsg_nosec net/socket.c:787 [inline]
__sock_sendmsg net/socket.c:802 [inline]
__sys_sendto+0x4a3/0x710 net/socket.c:2265
__do_sys_sendto net/socket.c:2272 [inline]
__se_sys_sendto net/socket.c:2268 [inline]
__x64_sys_sendto+0xde/0x100 net/socket.c:2268
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
&mm->mmap_lock --> &nsock->tx_lock --> sk_lock-AF_INET6

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sk_lock-AF_INET6);
lock(&nsock->tx_lock);
lock(sk_lock-AF_INET6);
rlock(&mm->mmap_lock);

*** DEADLOCK ***

2 locks held by syz.4.2801/16593:
#0: ffff888057aca0e8 (&ctx->tx_lock){+.+.}-{4:4}, at: tls_sw_sendmsg+0x130/0x2430 net/tls/tls_sw.c:1288
#1: ffff888055ac9d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
#1: ffff888055ac9d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: tls_sw_sendmsg+0x15d/0x2430 net/tls/tls_sw.c:1291

stack backtrace:
CPU: 0 UID: 0 PID: 16593 Comm: syz.4.2801 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
gup_fast_fallback+0x226/0x20d0 mm/gup.c:3193
__iov_iter_get_pages_alloc+0x370/0xa10 lib/iov_iter.c:1091
iov_iter_get_pages2+0x5e/0xa0 lib/iov_iter.c:1137
sk_msg_zerocopy_from_iter+0x22c/0x880 net/core/skmsg.c:328
tls_sw_sendmsg_locked net/tls/tls_sw.c:1140 [inline]
tls_sw_sendmsg+0x9f5/0x2430 net/tls/tls_sw.c:1292
sock_sendmsg_nosec net/socket.c:787 [inline]
__sock_sendmsg net/socket.c:802 [inline]
__sys_sendto+0x4a3/0x710 net/socket.c:2265
__do_sys_sendto net/socket.c:2272 [inline]
__se_sys_sendto net/socket.c:2268 [inline]
__x64_sys_sendto+0xde/0x100 net/socket.c:2268
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f75d6d5d60e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007f75d7bc6e88 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007f75d7bc86c0 RCX: 00007f75d6d5d60e
RDX: 0000000000000020 RSI: 00007f75d7bc7000 RDI: 0000000000000004
RBP: 0000000000000000 R08: 00007f75d7bc6f04 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
R13: 00007f75d7bc6f58 R14: 00007f75d7bc7000 R15: 0000000000000000
</TASK>


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