spi: spidev: fix a recursive locking error

When calling spidev_message() from the one of the ioctl() callbacks, the
spi_lock is already taken. When we then end up calling spidev_sync(), we
get the following splat:

[  214.047619]
[  214.049198] ============================================
[  214.054533] WARNING: possible recursive locking detected
[  214.059858] 6.2.0-rc3-0.0.0-devel+git.97ec4d55 #1 Not tainted
[  214.065969] --------------------------------------------
[  214.071290] spidev_test/1454 is trying to acquire lock:
[  214.076530] c4925dbc (&spidev->spi_lock){+.+.}-{3:3}, at: spidev_ioctl+0x8e0/0xab8
[  214.084164]
[  214.084164] but task is already holding lock:
[  214.090007] c4925dbc (&spidev->spi_lock){+.+.}-{3:3}, at: spidev_ioctl+0x44/0xab8
[  214.097537]
[  214.097537] other info that might help us debug this:
[  214.104075]  Possible unsafe locking scenario:
[  214.104075]
[  214.110004]        CPU0
[  214.112461]        ----
[  214.114916]   lock(&spidev->spi_lock);
[  214.118687]   lock(&spidev->spi_lock);
[  214.122457]
[  214.122457]  *** DEADLOCK ***
[  214.122457]
[  214.128386]  May be due to missing lock nesting notation
[  214.128386]
[  214.135183] 2 locks held by spidev_test/1454:
[  214.139553]  #0: c4925dbc (&spidev->spi_lock){+.+.}-{3:3}, at: spidev_ioctl+0x44/0xab8
[  214.147524]  #1: c4925e14 (&spidev->buf_lock){+.+.}-{3:3}, at: spidev_ioctl+0x70/0xab8
[  214.155493]
[  214.155493] stack backtrace:
[  214.159861] CPU: 0 PID: 1454 Comm: spidev_test Not tainted 6.2.0-rc3-0.0.0-devel+git.97ec4d55 #1
[  214.169012] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[  214.175555]  unwind_backtrace from show_stack+0x10/0x14
[  214.180819]  show_stack from dump_stack_lvl+0x60/0x90
[  214.185900]  dump_stack_lvl from __lock_acquire+0x874/0x2858
[  214.191584]  __lock_acquire from lock_acquire+0xfc/0x378
[  214.196918]  lock_acquire from __mutex_lock+0x9c/0x8a8
[  214.202083]  __mutex_lock from mutex_lock_nested+0x1c/0x24
[  214.207597]  mutex_lock_nested from spidev_ioctl+0x8e0/0xab8
[  214.213284]  spidev_ioctl from sys_ioctl+0x4d0/0xe2c
[  214.218277]  sys_ioctl from ret_fast_syscall+0x0/0x1c
[  214.223351] Exception stack(0xe75cdfa8 to 0xe75cdff0)
[  214.228422] dfa0:                   00000000 00001000 00000003 40206b00 bee266e8 bee266e0
[  214.236617] dfc0: 00000000 00001000 006a71a0 00000036 004c0040 004bfd18 00000000 00000003
[  214.244809] dfe0: 00000036 bee266c8 b6f16dc5 b6e8e5f6

Fix it by introducing an unlocked variant of spidev_sync() and calling it
from spidev_message() while other users who don't check the spidev->spi's
existence keep on using the locking flavor.

Reported-by: Francesco Dolcini <francesco@dolcini.it>
Fixes: 1f4d2dd4 ("spi: spidev: fix a race condition when accessing spidev->spi")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Tested-by: Max Krummenacher <max.krummenacher@toradex.com>
Link: https://lore.kernel.org/r/20230116144149.305560-1-brgl@bgdev.pl


Signed-off-by: Mark Brown <broonie@kernel.org>