[PATCH -next] spi: spidev: fix a recursive locking error

Bartosz Golaszewski
2023-01-16T14:54:34Z

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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.97ec4d559d93 #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.97ec4d559d93 #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: 1f4d2dd45b6e ("spi: spidev: fix a race condition when accessing spidev->spi")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
drivers/spi/spidev.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index 8ef22ebcde1f..892965ac8fdf 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -89,10 +89,22 @@ MODULE_PARM_DESC(bufsiz, "data bytes in biggest supported SPI message");

/*-------------------------------------------------------------------------*/

+static ssize_t
+spidev_sync_unlocked(struct spi_device *spi, struct spi_message *message)
+{
+ ssize_t status;
+
+ status = spi_sync(spi, message);
+ if (status == 0)
+ status = message->actual_length;
+
+ return status;
+}
+
static ssize_t
spidev_sync(struct spidev_data *spidev, struct spi_message *message)
{
- int status;
+ ssize_t status;
struct spi_device *spi;

mutex_lock(&spidev->spi_lock);
@@ -101,12 +113,10 @@ spidev_sync(struct spidev_data *spidev, struct spi_message *message)
if (spi == NULL)
status = -ESHUTDOWN;
else
- status = spi_sync(spi, message);
-
- if (status == 0)
- status = message->actual_length;
+ status = spidev_sync_unlocked(spi, message);

mutex_unlock(&spidev->spi_lock);
+
return status;
}

@@ -294,7 +304,7 @@ static int spidev_message(struct spidev_data *spidev,
spi_message_add_tail(k_tmp, &msg);
}

- status = spidev_sync(spidev, &msg);
+ status = spidev_sync_unlocked(spidev->spi, &msg);
if (status < 0)
goto done;

--
2.37.2