[syzbot] [rds?] possible deadlock in rds_tcp_tune (2)

[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=1171d95a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6259cfbe2d15cac4
dashboard link: https://syzkaller.appspot.com/bug?extid=2e2cf5331207053b8106
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+2e2cf5...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G U L
------------------------------------------------------
kworker/u10:8/15040 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: slab_pre_alloc_hook mm/slub.c:4452 [inline]
ffffffff8e9aaf80 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4807 [inline]
ffffffff8e9aaf80 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x4b/0x6f0 mm/slub.c:5334

but task is already holding lock:
ffff88805a3c1ce0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1709 [inline]
ffff88805a3c1ce0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: rds_tcp_tune+0xd7/0x930 net/rds/tcp.c:493

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #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]
slab_pre_alloc_hook mm/slub.c:4452 [inline]
slab_alloc_node mm/slub.c:4807 [inline]
__kmalloc_cache_noprof+0x4b/0x6f0 mm/slub.c:5334
kmalloc_noprof include/linux/slab.h:962 [inline]
kzalloc_noprof include/linux/slab.h:1200 [inline]
ref_tracker_alloc+0x190/0x590 lib/ref_tracker.c:270
__netns_tracker_alloc include/net/net_namespace.h:367 [inline]
netns_tracker_alloc include/net/net_namespace.h:376 [inline]
get_net_track include/net/net_namespace.h:393 [inline]
sk_net_refcnt_upgrade+0x1b4/0x360 net/core/sock.c:2395
rds_tcp_tune+0x2aa/0x930 net/rds/tcp.c:502
rds_tcp_accept_one+0x4b8/0xeb0 net/rds/tcp_listen.c:200
rds_tcp_accept_worker+0x41/0x60 net/rds/tcp.c:524
process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275
process_scheduled_works kernel/workqueue.c:3358 [inline]
worker_thread+0x5da/0xe40 kernel/workqueue.c:3439
kthread+0x370/0x450 kernel/kthread.c:467
ret_from_fork+0x754/0xd80 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 --> &nsock->tx_lock --> k-sk_lock-AF_INET6

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(k-sk_lock-AF_INET6);
lock(&nsock->tx_lock);
lock(k-sk_lock-AF_INET6);
lock(fs_reclaim);

*** DEADLOCK ***

4 locks held by kworker/u10:8/15040:
#0: ffff888033870148 ((wq_completion)krdsd){+.+.}-{0:0}, at: process_one_work+0x1287/0x1920 kernel/workqueue.c:3250
#1: ffffc90006ee7d08 ((work_completion)(&rtn->rds_tcp_accept_w)){+.+.}-{0:0}, at: process_one_work+0x93c/0x1920 kernel/workqueue.c:3251
#2: ffff888077acfc68 (&rtn->rds_tcp_accept_lock){+.+.}-{4:4}, at: rds_tcp_accept_one+0xb1/0xeb0 net/rds/tcp_listen.c:190
#3: ffff88805a3c1ce0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1709 [inline]
#3: ffff88805a3c1ce0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: rds_tcp_tune+0xd7/0x930 net/rds/tcp.c:493

stack backtrace:
CPU: 0 UID: 0 PID: 15040 Comm: kworker/u10:8 Tainted: G U L syzkaller #0 PREEMPT(full)
Tainted: [U]=USER, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: krdsd rds_tcp_accept_worker
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]
slab_pre_alloc_hook mm/slub.c:4452 [inline]
slab_alloc_node mm/slub.c:4807 [inline]
__kmalloc_cache_noprof+0x4b/0x6f0 mm/slub.c:5334
kmalloc_noprof include/linux/slab.h:962 [inline]
kzalloc_noprof include/linux/slab.h:1200 [inline]
ref_tracker_alloc+0x190/0x590 lib/ref_tracker.c:270
__netns_tracker_alloc include/net/net_namespace.h:367 [inline]
netns_tracker_alloc include/net/net_namespace.h:376 [inline]
get_net_track include/net/net_namespace.h:393 [inline]
sk_net_refcnt_upgrade+0x1b4/0x360 net/core/sock.c:2395
rds_tcp_tune+0x2aa/0x930 net/rds/tcp.c:502
rds_tcp_accept_one+0x4b8/0xeb0 net/rds/tcp_listen.c:200
rds_tcp_accept_worker+0x41/0x60 net/rds/tcp.c:524
process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275
process_scheduled_works kernel/workqueue.c:3358 [inline]
worker_thread+0x5da/0xe40 kernel/workqueue.c:3439
kthread+0x370/0x450 kernel/kthread.c:467
ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git main

This crash does not have a reproducer. I cannot test it.

>
> commit 4cd6716706210de3ed52d549ee784a12cc8ffe3a (HEAD)
> Author: Allison Henderson <ache...@kernel.org>
> Date: Thu Feb 26 12:45:39 2026 -0700
>
> net/rds: Fix circular locking dependency in rds_tcp_tune
>
> syzbot reported a circular locking dependency in rds_tcp_tune() where
> sk_net_refcnt_upgrade() is called while holding the socket lock:

>
> ======================================================
> WARNING: possible circular locking dependency detected

> ------------------------------------------------------
> kworker/u10:8/15040 is trying to acquire lock:

> ffffffff8e9aaf80 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x4b/0x6f0

>
> but task is already holding lock:

> ffff88805a3c1ce0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: rds_tcp_tune+0xd7/0x930
>
> The issue occurs because sk_net_refcnt_upgrade() performs memory allocation
> (via get_net_track() -> ref_tracker_alloc()) while the socket lock is held,
> creating a circular dependency with fs_reclaim.
>
> Fix this by moving sk_net_refcnt_upgrade() outside the socket lock critical
> section. Since the fresh socket is not yet exposed to other threads, no
> locks are needed at this time.
>
> Reported-by: syzbot+2e2cf5...@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2e2cf5331207053b8106
> Fixes: 5c70eb5c593d ("net: better track kernel sockets lifetime")
> Signed-off-by: Allison Henderson <ache...@kernel.org>
>
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 04f310255692..da22b3dfdbf0 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -490,18 +490,24 @@ bool rds_tcp_tune(struct socket *sock)
> commit 4cd6716706210de3ed52d549ee784a12cc8ffe3a (HEAD)
> Author: Allison Henderson <ache...@kernel.org>
> Date: Thu Feb 26 12:45:39 2026 -0700
>
> net/rds: Fix circular locking dependency in rds_tcp_tune
>
> syzbot reported a circular locking dependency in rds_tcp_tune() where
> sk_net_refcnt_upgrade() is called while holding the socket lock:

>
> ======================================================
> WARNING: possible circular locking dependency detected

> ------------------------------------------------------
> kworker/u10:8/15040 is trying to acquire lock:

> ffffffff8e9aaf80 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x4b/0x6f0

>
> but task is already holding lock:

> ffff88805a3c1ce0 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: rds_tcp_tune+0xd7/0x930
>
> The issue occurs because sk_net_refcnt_upgrade() performs memory allocation
> (via get_net_track() -> ref_tracker_alloc()) while the socket lock is held,
> creating a circular dependency with fs_reclaim.
>
> Fix this by moving sk_net_refcnt_upgrade() outside the socket lock critical
> section. Since the fresh socket is not yet exposed to other threads, no
> locks are needed at this time.
>
> Reported-by: syzbot+2e2cf5...@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2e2cf5331207053b8106
> Fixes: 5c70eb5c593d ("net: better track kernel sockets lifetime")
> Signed-off-by: Allison Henderson <ache...@kernel.org>
>
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 04f310255692..da22b3dfdbf0 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -490,18 +490,24 @@ bool rds_tcp_tune(struct socket *sock)
> struct rds_tcp_net *rtn;
>
> tcp_sock_set_nodelay(sock->sk);
> - lock_sock(sk);
> /* TCP timer functions might access net namespace even after
> * a process which created this net namespace terminated.
> */
> if (!sk->sk_net_refcnt) {
> - if (!maybe_get_net(net)) {
> - release_sock(sk);
> + if (!maybe_get_net(net))
> return false;
> - }
> + /*
> + * We call sk_net_refcnt_upgrade before the lock_sock since it is
> + * not yet shared, no lock is needed at this time. Further,
> + * because sk_net_refcnt_upgrade does a GFP_KERNEL allocation,
> + * this can trigger an fs_reclaim in other systems which creates
> + * a circular lock dependancy. Avoid this by upgrading the
> + * refcnt before the locking the socket.
> + */
> sk_net_refcnt_upgrade(sk);
> put_net(net);
> }
> + lock_sock(sk);
> rtn = net_generic(net, rds_tcp_netid);
> if (rtn->sndbuf_size > 0) {
> sk->sk_sndbuf = rtn->sndbuf_size;
> @@ -490,18 +490,24 @@ bool rds_tcp_tune(struct socket *sock)
> struct rds_tcp_net *rtn;
>
> tcp_sock_set_nodelay(sock->sk);
> - lock_sock(sk);
> /* TCP timer functions might access net namespace even after
> * a process which created this net namespace terminated.
> */
> if (!sk->sk_net_refcnt) {
> - if (!maybe_get_net(net)) {
> - release_sock(sk);
> + if (!maybe_get_net(net))
> return false;
> - }
> + /*
> + * We call sk_net_refcnt_upgrade before the lock_sock since it is
> + * not yet shared, no lock is needed at this time. Further,
> + * because sk_net_refcnt_upgrade does a GFP_KERNEL allocation,
> + * this can trigger an fs_reclaim in other systems which creates
> + * a circular lock dependancy. Avoid this by upgrading the
> + * refcnt before the locking the socket.
> + */
> sk_net_refcnt_upgrade(sk);
> put_net(net);
> }
> + lock_sock(sk);
> rtn = net_generic(net, rds_tcp_netid);
> if (rtn->sndbuf_size > 0) {
> sk->sk_sndbuf = rtn->sndbuf_size;
>