[syzbot] [mm?] possible deadlock in lock_mm_and_find_vma (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 32a92f8c8932 Convert more 'alloc_obj' cases to default GFP..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13cd6f3a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6259cfbe2d15cac4
dashboard link: https://syzkaller.appspot.com/bug?extid=709f5ab0e03871dec50a
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/64d473c704b2/disk-32a92f8c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/570c8f79c450/vmlinux-32a92f8c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b3d4ccd686ce/bzImage-32a92f8c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+709f5a...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.3.3387/17804 is trying to acquire lock:
ffffffff8e9aaf80 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:317 [inline]
ffffffff8e9aaf80 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x166/0x5f0 mm/page_alloc.c:5018

but task is already holding lock:
ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:611 [inline]
ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:441 [inline]
ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x35/0x6f0 mm/mmap_lock.c:501

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (&mm->mmap_lock){++++}-{4:4}:
__might_fault+0xde/0x140 mm/memory.c:7217
_inline_copy_from_user include/linux/uaccess.h:169 [inline]
_copy_from_user+0x29/0xd0 lib/usercopy.c:18
copy_from_user include/linux/uaccess.h:223 [inline]
copy_from_sockptr_offset include/linux/sockptr.h:48 [inline]
copy_from_sockptr include/linux/sockptr.h:61 [inline]
do_ip_setsockopt+0x2363/0x3200 net/ipv4/ip_sockglue.c:1294
ip_setsockopt+0x5a/0xf0 net/ipv4/ip_sockglue.c:1417
ipv6_setsockopt+0x155/0x170 net/ipv6/ipv6_sockglue.c:968
tcp_setsockopt+0xa7/0x100 net/ipv4/tcp.c:4217
smc_setsockopt+0x1b6/0xa10 net/smc/af_smc.c:3097
do_sock_setsockopt+0xf3/0x1d0 net/socket.c:2322
__sys_setsockopt+0x119/0x190 net/socket.c:2347
__do_sys_setsockopt net/socket.c:2353 [inline]
__se_sys_setsockopt net/socket.c:2350 [inline]
__x64_sys_setsockopt+0xbd/0x160 net/socket.c:2350
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (k-sk_lock-AF_INET6){+.+.}-{0:0}:
lock_sock_nested+0x41/0xf0 net/core/sock.c:3780
lock_sock include/net/sock.h:1709 [inline]
inet_shutdown+0x67/0x410 net/ipv4/af_inet.c:913
nbd_mark_nsock_dead+0xae/0x5c0 drivers/block/nbd.c:318
sock_shutdown+0x16b/0x200 drivers/block/nbd.c:411
nbd_clear_sock drivers/block/nbd.c:1427 [inline]
nbd_config_put+0x1eb/0x750 drivers/block/nbd.c:1451
nbd_release+0xb7/0x190 drivers/block/nbd.c:1756
blkdev_put_whole+0xb0/0xf0 block/bdev.c:737
bdev_release+0x47f/0x6d0 block/bdev.c:1160
blkdev_release+0x15/0x20 block/fops.c:705
__fput+0x3ff/0xb40 fs/file_table.c:469
task_work_run+0x150/0x240 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0x100/0x4a0 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
do_syscall_64+0x668/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x428/0x1080 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0x422/0x1e70 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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x23c/0x670 block/blk-mq.c:2386
blk_mq_dispatch_list+0x51d/0x1360 block/blk-mq.c:2949
blk_mq_flush_plug_list block/blk-mq.c:2997 [inline]
blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2969
__blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x584/0x6c0 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x562/0xc10 block/blk-core.c:753
submit_bio_noacct+0xd17/0x2010 block/blk-core.c:884
blk_crypto_submit_bio include/linux/blk-crypto.h:203 [inline]
submit_bh_wbc+0x59c/0x770 fs/buffer.c:2821
submit_bh fs/buffer.c:2826 [inline]
block_read_full_folio+0x4c8/0x8e0 fs/buffer.c:2458
filemap_read_folio+0xfc/0x3b0 mm/filemap.c:2496
do_read_cache_folio+0x2d7/0x6b0 mm/filemap.c:4096
read_mapping_folio include/linux/pagemap.h:1028 [inline]
read_part_sector+0xd1/0x370 block/partitions/core.c:723
adfspart_check_ICS+0x93/0x910 block/partitions/acorn.c:360
check_partition block/partitions/core.c:142 [inline]
blk_add_partitions block/partitions/core.c:590 [inline]
bdev_disk_changed+0x7f8/0xc80 block/partitions/core.c:694
blkdev_get_whole+0x187/0x290 block/bdev.c:764
bdev_open+0x2c7/0xe40 block/bdev.c:973
blkdev_open+0x34e/0x4f0 block/fops.c:697
do_dentry_open+0x6d8/0x1660 fs/open.c:949
vfs_open+0x82/0x3f0 fs/open.c:1081
do_open fs/namei.c:4671 [inline]
path_openat+0x208c/0x31a0 fs/namei.c:4830
do_file_open+0x20e/0x430 fs/namei.c:4859
do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0x12d/0x210 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&cmd->lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
nbd_queue_rq+0xba/0x1080 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0x422/0x1e70 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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x23c/0x670 block/blk-mq.c:2386
blk_mq_dispatch_list+0x51d/0x1360 block/blk-mq.c:2949
blk_mq_flush_plug_list block/blk-mq.c:2997 [inline]
blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2969
__blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x584/0x6c0 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x562/0xc10 block/blk-core.c:753
submit_bio_noacct+0xd17/0x2010 block/blk-core.c:884
blk_crypto_submit_bio include/linux/blk-crypto.h:203 [inline]
submit_bh_wbc+0x59c/0x770 fs/buffer.c:2821
submit_bh fs/buffer.c:2826 [inline]
block_read_full_folio+0x4c8/0x8e0 fs/buffer.c:2458
filemap_read_folio+0xfc/0x3b0 mm/filemap.c:2496
do_read_cache_folio+0x2d7/0x6b0 mm/filemap.c:4096
read_mapping_folio include/linux/pagemap.h:1028 [inline]
read_part_sector+0xd1/0x370 block/partitions/core.c:723
adfspart_check_ICS+0x93/0x910 block/partitions/acorn.c:360
check_partition block/partitions/core.c:142 [inline]
blk_add_partitions block/partitions/core.c:590 [inline]
bdev_disk_changed+0x7f8/0xc80 block/partitions/core.c:694
blkdev_get_whole+0x187/0x290 block/bdev.c:764
bdev_open+0x2c7/0xe40 block/bdev.c:973
blkdev_open+0x34e/0x4f0 block/fops.c:697
do_dentry_open+0x6d8/0x1660 fs/open.c:949
vfs_open+0x82/0x3f0 fs/open.c:1081
do_open fs/namei.c:4671 [inline]
path_openat+0x208c/0x31a0 fs/namei.c:4830
do_file_open+0x20e/0x430 fs/namei.c:4859
do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0x12d/0x210 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (set->srcu){.+.+}-{0:0}:
srcu_lock_sync include/linux/srcu.h:199 [inline]
__synchronize_srcu+0xa1/0x2a0 kernel/rcu/srcutree.c:1505
blk_mq_wait_quiesce_done block/blk-mq.c:284 [inline]
blk_mq_wait_quiesce_done block/blk-mq.c:281 [inline]
blk_mq_quiesce_queue block/blk-mq.c:304 [inline]
blk_mq_quiesce_queue+0x149/0x1c0 block/blk-mq.c:299
elevator_switch+0x17b/0x7e0 block/elevator.c:576
elevator_change+0x352/0x530 block/elevator.c:681
elevator_set_default+0x29e/0x360 block/elevator.c:754
blk_register_queue+0x412/0x590 block/blk-sysfs.c:940
__add_disk+0x73f/0xe40 block/genhd.c:528
add_disk_fwnode+0x118/0x5c0 block/genhd.c:597
add_disk include/linux/blkdev.h:785 [inline]
nbd_dev_add+0x77a/0xb10 drivers/block/nbd.c:1984
nbd_init+0x291/0x2b0 drivers/block/nbd.c:2692
do_one_initcall+0x11d/0x760 init/main.c:1382
do_initcall_level init/main.c:1444 [inline]
do_initcalls init/main.c:1460 [inline]
do_basic_setup init/main.c:1479 [inline]
kernel_init_freeable+0x6e5/0x7a0 init/main.c:1692
kernel_init+0x1f/0x1e0 init/main.c:1582
ret_from_fork+0x754/0xd80 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}:
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
queue_requests_store+0x38b/0x660 block/blk-sysfs.c:117
queue_attr_store+0x25f/0x2f0 block/blk-sysfs.c:866
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1070 fs/read_write.c:688
ksys_pwrite64 fs/read_write.c:795 [inline]
__do_sys_pwrite64 fs/read_write.c:803 [inline]
__se_sys_pwrite64 fs/read_write.c:800 [inline]
__x64_sys_pwrite64+0x1eb/0x250 fs/read_write.c:800
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#26){++++}-{0:0}:
blk_alloc_queue+0x610/0x790 block/blk-core.c:461
blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4429
__blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4476
loop_add+0x498/0xb60 drivers/block/loop.c:2049
loop_init+0x1d3/0x200 drivers/block/loop.c:2288
do_one_initcall+0x11d/0x760 init/main.c:1382
do_initcall_level init/main.c:1444 [inline]
do_initcalls init/main.c:1460 [inline]
do_basic_setup init/main.c:1479 [inline]
kernel_init_freeable+0x6e5/0x7a0 init/main.c:1692
kernel_init+0x1f/0x1e0 init/main.c:1582
ret_from_fork+0x754/0xd80 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 kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
__fs_reclaim_acquire mm/page_alloc.c:4348 [inline]
fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4362
might_alloc include/linux/sched/mm.h:317 [inline]
prepare_alloc_pages+0x166/0x5f0 mm/page_alloc.c:5018
__alloc_frozen_pages_noprof+0x19a/0x2ba0 mm/page_alloc.c:5239
alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2484
alloc_frozen_pages_noprof mm/mempolicy.c:2555 [inline]
alloc_pages_noprof+0x131/0x390 mm/mempolicy.c:2575
pagetable_alloc_noprof include/linux/mm.h:3404 [inline]
pmd_alloc_one_noprof include/asm-generic/pgalloc.h:143 [inline]
__pmd_alloc+0x3b/0x9c0 mm/memory.c:6709
pmd_alloc include/linux/mm.h:3320 [inline]
__handle_mm_fault+0xa99/0x2b60 mm/memory.c:6406
handle_mm_fault+0x36d/0xa20 mm/memory.c:6623
do_user_addr_fault+0x74c/0x12f0 arch/x86/mm/fault.c:1385
handle_page_fault arch/x86/mm/fault.c:1474 [inline]
exc_page_fault+0x6f/0xd0 arch/x86/mm/fault.c:1527
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
rep_movs_alternative+0x30/0x90 arch/x86/lib/copy_user_64.S:53
copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
raw_copy_from_user arch/x86/include/asm/uaccess_64.h:141 [inline]
_inline_copy_from_user include/linux/uaccess.h:185 [inline]
_copy_from_user+0x98/0xd0 lib/usercopy.c:18
copy_from_user include/linux/uaccess.h:223 [inline]
get_user_ifreq+0x77/0x1c0 net/socket.c:3350
br_ioctl_stub+0x23d/0x4d0 net/bridge/br_ioctl.c:409
br_ioctl_call+0x53/0xa0 net/socket.c:1227
sock_ioctl+0x616/0x6b0 net/socket.c:1329
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 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:
fs_reclaim --> k-sk_lock-AF_INET6 --> &mm->mmap_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(&mm->mmap_lock);
lock(k-sk_lock-AF_INET6);
lock(&mm->mmap_lock);
lock(fs_reclaim);

*** DEADLOCK ***

2 locks held by syz.3.3387/17804:
#0: ffffffff905e2228 (br_ioctl_mutex){+.+.}-{4:4}, at: br_ioctl_call+0x34/0xa0 net/socket.c:1225
#1: ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:611 [inline]
#1: ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:441 [inline]
#1: ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x35/0x6f0 mm/mmap_lock.c:501

stack backtrace:
CPU: 0 UID: 0 PID: 17804 Comm: syz.3.3387 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
check_noncircular+0x146/0x160 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+0x14b8/0x2630 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
__fs_reclaim_acquire mm/page_alloc.c:4348 [inline]
fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4362
might_alloc include/linux/sched/mm.h:317 [inline]
prepare_alloc_pages+0x166/0x5f0 mm/page_alloc.c:5018
__alloc_frozen_pages_noprof+0x19a/0x2ba0 mm/page_alloc.c:5239
alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2484
alloc_frozen_pages_noprof mm/mempolicy.c:2555 [inline]
alloc_pages_noprof+0x131/0x390 mm/mempolicy.c:2575
pagetable_alloc_noprof include/linux/mm.h:3404 [inline]
pmd_alloc_one_noprof include/asm-generic/pgalloc.h:143 [inline]
__pmd_alloc+0x3b/0x9c0 mm/memory.c:6709
pmd_alloc include/linux/mm.h:3320 [inline]
__handle_mm_fault+0xa99/0x2b60 mm/memory.c:6406
handle_mm_fault+0x36d/0xa20 mm/memory.c:6623
do_user_addr_fault+0x74c/0x12f0 arch/x86/mm/fault.c:1385
handle_page_fault arch/x86/mm/fault.c:1474 [inline]
exc_page_fault+0x6f/0xd0 arch/x86/mm/fault.c:1527
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0010:rep_movs_alternative+0x30/0x90 arch/x86/lib/copy_user_64.S:60
Code: 83 f9 08 73 25 85 c9 74 0f 8a 06 88 07 48 ff c7 48 ff c6 48 ff c9 75 f1 e9 bd 93 04 00 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 <48> 8b 06 48 89 07 48 83 c6 08 48 83 c7 08 83 e9 08 74 db 83 f9 08
RSP: 0018:ffffc900044e7c18 EFLAGS: 00050202
RAX: 0000000000000001 RBX: 0000000000000008 RCX: 0000000000000028
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffffc900044e7cd0
RBP: 0000000000000028 R08: 0000000000000001 R09: fffff5200089cf9e
R10: ffffc900044e7cf7 R11: 0000000000000001 R12: 0000000000000000
R13: ffffc900044e7cd0 R14: ffffc900044e7cd0 R15: 0000000000000000
copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
raw_copy_from_user arch/x86/include/asm/uaccess_64.h:141 [inline]
_inline_copy_from_user include/linux/uaccess.h:185 [inline]
_copy_from_user+0x98/0xd0 lib/usercopy.c:18
copy_from_user include/linux/uaccess.h:223 [inline]
get_user_ifreq+0x77/0x1c0 net/socket.c:3350
br_ioctl_stub+0x23d/0x4d0 net/bridge/br_ioctl.c:409
br_ioctl_call+0x53/0xa0 net/socket.c:1227
sock_ioctl+0x616/0x6b0 net/socket.c:1329
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9f4239c629
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9f432ed028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9f42616180 RCX: 00007f9f4239c629
RDX: 0000000000000008 RSI: 00000000000089a2 RDI: 0000000000000003
RBP: 00007f9f42432b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9f42616218 R14: 00007f9f42616180 R15: 00007ffd31101248
</TASK>
----------------
Code disassembly (best guess):
0: 83 f9 08 cmp $0x8,%ecx
3: 73 25 jae 0x2a
5: 85 c9 test %ecx,%ecx
7: 74 0f je 0x18
9: 8a 06 mov (%rsi),%al
b: 88 07 mov %al,(%rdi)
d: 48 ff c7 inc %rdi
10: 48 ff c6 inc %rsi
13: 48 ff c9 dec %rcx
16: 75 f1 jne 0x9
18: e9 bd 93 04 00 jmp 0x493da
1d: 66 66 2e 0f 1f 84 00 data16 cs nopw 0x0(%rax,%rax,1)
24: 00 00 00 00
28: 66 90 xchg %ax,%ax
* 2a: 48 8b 06 mov (%rsi),%rax <-- trapping instruction
2d: 48 89 07 mov %rax,(%rdi)
30: 48 83 c6 08 add $0x8,%rsi
34: 48 83 c7 08 add $0x8,%rdi
38: 83 e9 08 sub $0x8,%ecx
3b: 74 db je 0x18
3d: 83 f9 08 cmp $0x8,%ecx


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[Pedro Falcato]

+Cc netdev, block, nbd people

It looks to me like the issue is:
setsockopt(nbd_sock) -> takes sk_lock -> copy_from_user -> page fault ->
mmap_lock -> allocation needs reclaim -> fs_reclaim -> fs does IO -> nbd
grabs sk_lock -> deadlock

Looks longstanding. No idea why it's finding it only now.

I would suggest something like this, if the diagnosis is correct
(plus adapting all callers):

diff --git a/net/core/sock.c b/net/core/sock.c
index 5976100a9d55..8a100c404c8e 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1140,8 +1140,10 @@ sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
}
#endif

-void sockopt_lock_sock(struct sock *sk)
+__must_check unsigned int sockopt_lock_sock(struct sock *sk)
{
+ unsigned int flags = 0;
+
/* When current->bpf_ctx is set, the setsockopt is called from
* a bpf prog. bpf has ensured the sk lock has been
* acquired before calling setsockopt().
@@ -1149,15 +1151,27 @@ void sockopt_lock_sock(struct sock *sk)
if (has_current_bpf_ctx())
return;

+ if (!(sk->sk_allocation & __GFP_IO)) {
+ /* If the socket cannot tolerate IO for its own allocations,
+ * it's almost certain it will not be able to tolerate IO under
+ * lock_sock(). However, sockopt code likes to possibly trigger
+ * reclaim (due to page faults) under lock_sock(), and that can
+ * uncontrollably do IO.
+ */
+ flags = memalloc_noio_save();
+ }
+
lock_sock(sk);
+ return flags;
}
EXPORT_SYMBOL(sockopt_lock_sock);

-void sockopt_release_sock(struct sock *sk)
+void sockopt_release_sock(struct sock *sk, unsigned int memalloc_flags)
{
if (has_current_bpf_ctx())
return;

+ memalloc_noio_restore(memalloc_flags);
release_sock(sk);
}
EXPORT_SYMBOL(sockopt_release_sock);



I would send it, but I would like to get some sort of repro first, at least
on my end.

--
Pedro

[Pedro Falcato]

On Thu, Feb 26, 2026 at 05:40:26PM +0000, Pedro Falcato wrote:
> +Cc netdev, block, nbd people
>
> On Thu, Feb 26, 2026 at 06:54:27AM -0800, syzbot wrote:

> <snip>

> >
> > Chain exists of:
> > fs_reclaim --> k-sk_lock-AF_INET6 --> &mm->mmap_lock
> >
> > Possible unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > rlock(&mm->mmap_lock);
> > lock(k-sk_lock-AF_INET6);
> > lock(&mm->mmap_lock);
> > lock(fs_reclaim);
> >
> > *** DEADLOCK ***
> >
> > 2 locks held by syz.3.3387/17804:
> > #0: ffffffff905e2228 (br_ioctl_mutex){+.+.}-{4:4}, at: br_ioctl_call+0x34/0xa0 net/socket.c:1225
> > #1: ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:611 [inline]
> > #1: ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:441 [inline]
> > #1: ffff88807ad4b440 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x35/0x6f0 mm/mmap_lock.c:501
> >
>
> It looks to me like the issue is:
> setsockopt(nbd_sock) -> takes sk_lock -> copy_from_user -> page fault ->
> mmap_lock -> allocation needs reclaim -> fs_reclaim -> fs does IO -> nbd
> grabs sk_lock -> deadlock
>

Another funny case that came to me just now:
sendmsg(nbd_sock) -> lock_sock(nbd_sock) -> tcp_sendmsg_locked(nbd_sock) ->
copy_from_user() -> if VMA is backed by file on nbd bdev -> ... ->
lock_sock(nbd_sock)

Right? Is there something extremely crucial that I'm missing?

--
Pedro