[v6.6] possible deadlock in iter_file_splice_write

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6436c12a2ced Linux 6.6.150
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14ddbe49580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=189d50097eda9bb61103
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f01168de2d4b/disk-6436c12a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e63b80c9c349/vmlinux-6436c12a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9297ad58728c/bzImage-6436c12a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+189d50...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.6047/27572 is trying to acquire lock:
ffff888053f4c068 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x1ba/0xcf0 fs/splice.c:683

but task is already holding lock:
ffff88802559a418 (sb_writers#5){.+.+}-{0:0}, at: __do_splice fs/splice.c:1370 [inline]
ffff88802559a418 (sb_writers#5){.+.+}-{0:0}, at: __do_sys_splice fs/splice.c:1586 [inline]
ffff88802559a418 (sb_writers#5){.+.+}-{0:0}, at: __se_sys_splice+0x398/0x4a0 fs/splice.c:1568

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (sb_writers#5){.+.+}-{0:0}:
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1633 [inline]
sb_start_write+0x4d/0x1c0 include/linux/fs.h:1708
mnt_want_write+0x41/0x90 fs/namespace.c:412
open_last_lookups fs/namei.c:3596 [inline]
path_openat+0x768/0x3270 fs/namei.c:3841
do_filp_open+0x1f2/0x430 fs/namei.c:3871
file_open_name fs/open.c:1367 [inline]
filp_open+0x180/0x1e0 fs/open.c:1387
nvmet_file_ns_enable+0x74/0x330 drivers/nvme/target/io-cmd-file.c:41
nvmet_ns_enable+0xf4/0x8c0 drivers/nvme/target/core.c:578
nvmet_ns_enable_store+0xd8/0x170 drivers/nvme/target/configfs.c:549
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x312/0x400 fs/configfs/file.c:229
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x474/0x9a0 fs/read_write.c:584
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #5 (&subsys->lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
nvmet_ns_device_path_store+0x54/0x150 drivers/nvme/target/configfs.c:350
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x312/0x400 fs/configfs/file.c:229
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x474/0x9a0 fs/read_write.c:584
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #4 (&p->frag_sem){.+.+}-{3:3}:
down_read+0x46/0x2e0 kernel/locking/rwsem.c:1520
flush_write_buffer fs/configfs/file.c:205 [inline]
configfs_write_iter+0x215/0x400 fs/configfs/file.c:229
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x474/0x9a0 fs/read_write.c:584
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #3 (&buffer->mutex#2){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
configfs_read_iter+0x72/0x570 fs/configfs/file.c:86
__kernel_read+0x2e5/0x730 fs/read_write.c:428
integrity_kernel_read+0x8a/0xd0 security/integrity/iint.c:221
ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:485 [inline]
ima_calc_file_shash security/integrity/ima/ima_crypto.c:516 [inline]
ima_calc_file_hash+0xb1f/0x1960 security/integrity/ima/ima_crypto.c:573
ima_collect_measurement+0x4d4/0xa30 security/integrity/ima/ima_api.c:290
process_measurement+0x123a/0x1d50 security/integrity/ima/ima_main.c:370
ima_file_check+0xcc/0x110 security/integrity/ima/ima_main.c:568
do_open fs/namei.c:3685 [inline]
path_openat+0x2910/0x3270 fs/namei.c:3844
do_filp_open+0x1f2/0x430 fs/namei.c:3871
do_sys_openat2+0x134/0x1d0 fs/open.c:1422
do_sys_open fs/open.c:1437 [inline]
__do_sys_openat fs/open.c:1453 [inline]
__se_sys_openat fs/open.c:1448 [inline]
__x64_sys_openat+0x139/0x160 fs/open.c:1448
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #2 (&iint_mutex_key[depth]){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
process_measurement+0x739/0x1d50 security/integrity/ima/ima_main.c:275
ima_file_check+0xcc/0x110 security/integrity/ima/ima_main.c:568
do_open fs/namei.c:3685 [inline]
path_openat+0x2910/0x3270 fs/namei.c:3844
do_file_open_root+0x2f3/0x5a0 fs/namei.c:3896
file_open_root+0x167/0x1c0 fs/open.c:1402
kernel_read_file_from_path_initns+0x151/0x230 fs/kernel_read_file.c:163
fw_get_filesystem_firmware drivers/base/firmware_loader/main.c:548 [inline]
_request_firmware+0xb43/0x1520 drivers/base/firmware_loader/main.c:911
request_firmware+0x36/0x50 drivers/base/firmware_loader/main.c:987
reg_reload_regdb+0x9a/0x490 net/wireless/reg.c:1078
genl_family_rcv_msg_doit+0x21a/0x310 net/netlink/genetlink.c:971
genl_family_rcv_msg net/netlink/genetlink.c:1051 [inline]
genl_rcv_msg+0x611/0x7a0 net/netlink/genetlink.c:1066
netlink_rcv_skb+0x235/0x4c0 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1075
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x7b1/0x930 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x8d0/0xbf0 net/netlink/af_netlink.c:1899
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
____sys_sendmsg+0x61b/0x980 net/socket.c:2595
___sys_sendmsg+0x2a6/0x360 net/socket.c:2649
__sys_sendmsg net/socket.c:2678 [inline]
__do_sys_sendmsg net/socket.c:2687 [inline]
__se_sys_sendmsg+0x1d0/0x2c0 net/socket.c:2685
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (cb_lock){++++}-{3:3}:
down_read+0x46/0x2e0 kernel/locking/rwsem.c:1520
genl_rcv+0x19/0x40 net/netlink/genetlink.c:1074
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x7b1/0x930 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x8d0/0xbf0 net/netlink/af_netlink.c:1899
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
sock_sendmsg+0x23b/0x3a0 net/socket.c:768
splice_to_socket+0xb92/0x1270 fs/splice.c:881
do_splice_from fs/splice.c:933 [inline]
do_splice+0xe45/0x1b20 fs/splice.c:1292
__do_splice fs/splice.c:1370 [inline]
__do_sys_splice fs/splice.c:1586 [inline]
__se_sys_splice+0x398/0x4a0 fs/splice.c:1568
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (&pipe->mutex/1){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
iter_file_splice_write+0x1ba/0xcf0 fs/splice.c:683
do_splice_from fs/splice.c:933 [inline]
do_splice+0xe45/0x1b20 fs/splice.c:1292
__do_splice fs/splice.c:1370 [inline]
__do_sys_splice fs/splice.c:1586 [inline]
__se_sys_splice+0x398/0x4a0 fs/splice.c:1568
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
&pipe->mutex/1 --> &subsys->lock --> sb_writers#5

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(sb_writers#5);
lock(&subsys->lock);
lock(sb_writers#5);
lock(&pipe->mutex/1);

*** DEADLOCK ***

1 lock held by syz.0.6047/27572:
#0: ffff88802559a418 (sb_writers#5){.+.+}-{0:0}, at: __do_splice fs/splice.c:1370 [inline]
#0: ffff88802559a418 (sb_writers#5){.+.+}-{0:0}, at: __do_sys_splice fs/splice.c:1586 [inline]
#0: ffff88802559a418 (sb_writers#5){.+.+}-{0:0}, at: __se_sys_splice+0x398/0x4a0 fs/splice.c:1568

stack backtrace:
CPU: 1 PID: 27572 Comm: syz.0.6047 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
iter_file_splice_write+0x1ba/0xcf0 fs/splice.c:683
do_splice_from fs/splice.c:933 [inline]
do_splice+0xe45/0x1b20 fs/splice.c:1292
__do_splice fs/splice.c:1370 [inline]
__do_sys_splice fs/splice.c:1586 [inline]
__se_sys_splice+0x398/0x4a0 fs/splice.c:1568
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f62c3f9e0d9
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:00007f62c1db2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007f62c4226270 RCX: 00007f62c3f9e0d9
RDX: 0000000000000008 RSI: 0000000000000000 RDI: 0000000000000009
RBP: 00007f62c4035024 R08: 0000000040010003 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f62c4226308 R14: 00007f62c4226270 R15: 00007fff1e71e518
</TASK>


---
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