[BUG] Possible circular locking dependency in spidev (buf_lock <-> spi_lock)

홍유진 (YJ Hong)
2026-02-28T03:38:21Z

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Hello,

I am seeing a lockdep warning in spidev reporting a possible circular
locking dependency between buf_lock and spi_lock.

Kernel:
6.12.23

Lockdep warning:

[ 60.977069] WARNING: possible circular locking dependency detected
[ 60.996180] spidev_test_tel/256 is trying to acquire lock:
[ 61.001656] ffff0001a123fa78 (&spidev->spi_lock){+.+.}-{3:3}, at: spidev_sync+0x2c/0x70
[ 61.009674]
[ 61.015495] but task is already holding lock:
[ 61.015495] ffff0001a123fb30 (&spidev->buf_lock){+.+.}-{3:3}, at: spidev_write+0x44/0x13c
[ 61.023679]
[ 61.039314] the existing dependency chain (in reverse order) is:
[ 61.039314]
[ 61.039314] -> #1 (&spidev->buf_lock){+.+.}-{3:3}:
[ 61.054114] spidev_ioctl+0x80/0x718
[ 61.058205] __arm64_sys_ioctl+0x94/0xd8
...
[ 61.094760] -> #0 (&spidev->spi_lock){+.+.}-{3:3}:
[ 61.111988] spidev_sync+0x2c/0x70
[ 61.120342] spidev_write+0x104/0x13c

From inspection of the locking paths:

Path 1 (write/read):
spidev_write()
mutex_lock(&spidev->buf_lock)
-> spidev_sync()
mutex_lock(&spidev->spi_lock)

Lock order: buf_lock -> spi_lock

Path 2 (ioctl):
spidev_ioctl()
mutex_lock(&spidev->spi_lock)
mutex_lock(&spidev->buf_lock)

Lock order: spi_lock -> buf_lock

This results in an apparent lock ordering inversion:

buf_lock -> spi_lock
spi_lock -> buf_lock

Lockdep reports this as a possible circular dependency,
with the scenario:

CPU0: lock(buf_lock) -> lock(spi_lock)
CPU1: lock(spi_lock) -> lock(buf_lock)

I intentionally added an artificial delay in spidev_write()
before copy_from_user() to enlarge the timing window.

Then I executed concurrent operations on the same device
(spidev0.0):

Thread A: write()
Thread B: ioctl()

This reliably results in an actual deadlock:

CPU0: lock(buf_lock) -> waiting for spi_lock
CPU1: lock(spi_lock) -> waiting for buf_lock

The system becomes permanently blocked.

My questions:

1. Is this locking order intentional and considered safe?
2. Is this a known lockdep false positive?

Thanks,

Yujin Hong

[이미지]

홍유진 (Yujin Hong)

SW Development Group / Core BSP2 Team / Manager

yj.hong@telechips.com<mailto:lkj@telechips.com>

M +82-2-3017-5728

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[ 60.977069] WARNING: possible circular locking dependency detected
[ 60.985575] 6.12.23-telechips+ #56 Not tainted
[ 60.990011] ------------------------------------------------------
[ 60.996180] spidev_test_tel/256 is trying to acquire lock:
[ 61.001656] ffff0001a123fa78 (&spidev->spi_lock){+.+.}-{3:3}, at: spidev_sync+0x2c/0x70
[ 61.009674]
[ 61.009674] but task is already holding lock:
[ 61.015495] ffff0001a123fb30 (&spidev->buf_lock){+.+.}-{3:3}, at: spidev_write+0x44/0x13c
[ 61.023679]
[ 61.023679] which lock already depends on the new lock.
[ 61.023679]
[ 61.031843]
[ 61.031843] the existing dependency chain (in reverse order) is:
[ 61.039314]
[ 61.039314] -> #1 (&spidev->buf_lock){+.+.}-{3:3}:
[ 61.045582] __mutex_lock+0xa4/0xfc0
[ 61.049676] mutex_lock_nested+0x24/0x30
[ 61.054114] spidev_ioctl+0x80/0x718
[ 61.058205] __arm64_sys_ioctl+0x94/0xd8
[ 61.062644] invoke_syscall+0x44/0x100
[ 61.066912] el0_svc_common.constprop.0+0x40/0xe0
[ 61.072131] do_el0_svc+0x1c/0x28
[ 61.075961] el0_svc+0x48/0x114
[ 61.079617] el0t_64_sync_handler+0xc0/0xc4
[ 61.084314] el0t_64_sync+0x190/0x194
[ 61.088491]
[ 61.088491] -> #0 (&spidev->spi_lock){+.+.}-{3:3}:
[ 61.094760] __lock_acquire+0x1394/0x1cc8
[ 61.099284] lock_acquire+0x11c/0x324
[ 61.103460] __mutex_lock+0xa4/0xfc0
[ 61.107550] mutex_lock_nested+0x24/0x30
[ 61.111988] spidev_sync+0x2c/0x70
[ 61.115905] spidev_sync_write+0x9c/0xc0
[ 61.120342] spidev_write+0x104/0x13c
[ 61.124520] vfs_write+0xd4/0x5a4
[ 61.128351] ksys_write+0xe0/0xf8
[ 61.132181] __arm64_sys_write+0x1c/0x28
[ 61.136619] invoke_syscall+0x44/0x100
[ 61.140883] el0_svc_common.constprop.0+0x40/0xe0
[ 61.146102] do_el0_svc+0x1c/0x28
[ 61.149933] el0_svc+0x48/0x114
[ 61.153588] el0t_64_sync_handler+0xc0/0xc4
[ 61.158285] el0t_64_sync+0x190/0x194
[ 61.162461]
[ 61.162461] other info that might help us debug this:
[ 61.162461]
[ 61.170452] Possible unsafe locking scenario:
[ 61.170452]
[ 61.176361] CPU0 CPU1
[ 61.180880] ---- ----
[ 61.185400] lock(&spidev->buf_lock);
[ 61.189145] lock(&spidev->spi_lock);
[ 61.195406] lock(&spidev->buf_lock);
[ 61.201667] lock(&spidev->spi_lock);
[ 61.205412]
[ 61.205412] *** DEADLOCK ***
[ 61.205412]
[ 61.211320] 1 lock held by spidev_test_tel/256:
[ 61.215841] #0: ffff0001a123fb30 (&spidev->buf_lock){+.+.}-{3:3}, at: spidev_write+0x44/0x13c
[ 61.224461]
[ 61.224461] stack backtrace:
[ 61.228809] CPU: 3 UID: 0 PID: 256 Comm: spidev_test_tel Not tainted 6.12.23-telechips+ #56
[ 61.228815] Hardware name: Telechips TCC8070 LPD4X322 Main Core (DT)
[ 61.228819] Call trace:
[ 61.228821] dump_backtrace+0x9c/0x11c
[ 61.228829] show_stack+0x18/0x24
[ 61.228836] dump_stack_lvl+0xa4/0xf4
[ 61.228842] dump_stack+0x18/0x24
[ 61.228846] print_circular_bug.isra.0+0x364/0x44c
[ 61.228854] check_noncircular+0x184/0x198
[ 61.228861] __lock_acquire+0x1394/0x1cc8
[ 61.228866] lock_acquire+0x11c/0x324
[ 61.228870] __mutex_lock+0xa4/0xfc0
[ 61.228877] mutex_lock_nested+0x24/0x30
[ 61.228883] spidev_sync+0x2c/0x70
[ 61.228889] spidev_sync_write+0x9c/0xc0
[ 61.228895] spidev_write+0x104/0x13c
[ 61.228901] vfs_write+0xd4/0x5a4
[ 61.228907] ksys_write+0xe0/0xf8
[ 61.228914] __arm64_sys_write+0x1c/0x28
[ 61.228920] invoke_syscall+0x44/0x100
[ 61.228926] el0_svc_common.constprop.0+0x40/0xe0
[ 61.228933] do_el0_svc+0x1c/0x28
[ 61.228939] el0_svc+0x48/0x114
[ 61.228943] el0t_64_sync_handler+0xc0/0xc4
[ 61.228949] el0t_64_sync+0x190/0x194