Lockdep complains about possible circular locking dependencies when the
i.MX SDMA driver issues console messages under its spinlock. While the
SDMA driver calls back into the UART when issuing a message, the i.MX
UART driver will never call back into the SDMA driver for this UART,
because DMA is explicitly not used for UARTs providing the console.
To avoid the lockdep warnings put the UART port lock for console devices
into a separate subclass.
This fixes possible deadlock warnings like the following which was
provoked by adding a printk to the i.MX SDMA driver at a place where the
driver holds its spinlock.
======================================================
WARNING: possible circular locking dependency detected
6.6.0-rc3-00045-g517852be693b-dirty #110 Not tainted
------------------------------------------------------
swapper/0/0 is trying to acquire lock:
c1818e04 (console_owner){-...}-{0:0}, at: console_flush_all+0x1c4/0x634
but task is already holding lock:
c44649e0 (&vc->lock){-...}-{3:3}, at: sdma_int_handler+0xc4/0x368
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&vc->lock){-...}-{3:3}:
_raw_spin_lock_irqsave+0x4c/0x68
sdma_prep_dma_cyclic+0x1a8/0x21c
imx_uart_startup+0x44c/0x5d4
uart_startup+0x120/0x2b0
uart_port_activate+0x44/0x98
tty_port_open+0x80/0xd0
uart_open+0x18/0x20
tty_open+0x120/0x664
chrdev_open+0xc0/0x214
do_dentry_open+0x1d0/0x544
path_openat+0xbb0/0xea0
do_filp_open+0x5c/0xd4
do_sys_openat2+0xb8/0xf0
sys_openat+0x8c/0xd8
ret_fast_syscall+0x0/0x1c
-> #1 (&port_lock_key){-.-.}-{3:3}:
_raw_spin_lock_irqsave+0x4c/0x68
imx_uart_console_write+0x164/0x1a0
console_flush_all+0x220/0x634
console_unlock+0x64/0x164
vprintk_emit+0xb0/0x390
vprintk_default+0x24/0x2c
_printk+0x2c/0x5c
register_console+0x244/0x478
serial_core_register_port+0x5c4/0x618
imx_uart_probe+0x4e0/0x7d4
platform_probe+0x58/0xb0
really_probe+0xc4/0x2e0
__driver_probe_device+0x84/0x1a0
driver_probe_device+0x2c/0x108
__driver_attach+0x94/0x17c
bus_for_each_dev+0x7c/0xd0
bus_add_driver+0xc4/0x1cc
driver_register+0x7c/0x114
imx_uart_init+0x20/0x40
do_one_initcall+0x7c/0x3c4
kernel_init_freeable+0x17c/0x228
kernel_init+0x14/0x140
ret_from_fork+0x14/0x24
-> #0 (console_owner){-...}-{0:0}:
__lock_acquire+0x14b0/0x29a0
lock_acquire.part.0+0xb4/0x264
console_flush_all+0x20c/0x634
console_unlock+0x64/0x164
vprintk_emit+0xb0/0x390
vprintk_default+0x24/0x2c
_printk+0x2c/0x5c
sdma_int_handler+0xcc/0x368
__handle_irq_event_percpu+0x94/0x2d0
handle_irq_event+0x38/0xd0
handle_fasteoi_irq+0x98/0x248
handle_irq_desc+0x1c/0x2c
gic_handle_irq+0x6c/0x90
generic_handle_arch_irq+0x2c/0x64
__irq_svc+0x90/0xbc
cpuidle_enter_state+0x1a0/0x4f4
cpuidle_enter+0x30/0x40
do_idle+0x210/0x2b4
cpu_startup_entry+0x28/0x2c
rest_init+0xd0/0x184
arch_post_acpi_subsys_init+0x0/0x8
other info that might help us debug this:
Chain exists of:
console_owner --> &port_lock_key --> &vc->lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&vc->lock);
lock(&port_lock_key);
lock(&vc->lock);
lock(console_owner);
*** DEADLOCK ***
3 locks held by swapper/0/0:
#0: c44649e0 (&vc->lock){-...}-{3:3}, at: sdma_int_handler+0xc4/0x368
#1: c1818d50 (console_lock){+.+.}-{0:0}, at: vprintk_default+0x24/0x2c
#2: c1818d08 (console_srcu){....}-{0:0}, at: console_flush_all+0x44/0x634
stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.6.0-rc3-00045-g517852be693b-dirty #110
Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
unwind_backtrace from show_stack+0x10/0x14
show_stack from dump_stack_lvl+0x60/0x90
dump_stack_lvl from check_noncircular+0x184/0x1b8
check_noncircular from __lock_acquire+0x14b0/0x29a0
__lock_acquire from lock_acquire.part.0+0xb4/0x264
lock_acquire.part.0 from console_flush_all+0x20c/0x634
console_flush_all from console_unlock+0x64/0x164
console_unlock from vprintk_emit+0xb0/0x390
vprintk_emit from vprintk_default+0x24/0x2c
vprintk_default from _printk+0x2c/0x5c
_printk from sdma_int_handler+0xcc/0x368
sdma_int_handler from __handle_irq_event_percpu+0x94/0x2d0
__handle_irq_event_percpu from handle_irq_event+0x38/0xd0
handle_irq_event from handle_fasteoi_irq+0x98/0x248
handle_fasteoi_irq from handle_irq_desc+0x1c/0x2c
handle_irq_desc from gic_handle_irq+0x6c/0x90
gic_handle_irq from generic_handle_arch_irq+0x2c/0x64
generic_handle_arch_irq from __irq_svc+0x90/0xbc
Exception stack(0xc1801ee8 to 0xc1801f30)
1ee0: ffffffff ffffffff 00000001 00030349 00000000 00000012
1f00: 00000000 d7e45f4b 00000012 00000000 d7e16d63 c1810828 00000000 c1801f38
1f20: c108125c c1081260 60010013 ffffffff
__irq_svc from cpuidle_enter_state+0x1a0/0x4f4
cpuidle_enter_state from cpuidle_enter+0x30/0x40
cpuidle_enter from do_idle+0x210/0x2b4
do_idle from cpu_startup_entry+0x28/0x2c
cpu_startup_entry from rest_init+0xd0/0x184
rest_init from arch_post_acpi_subsys_init+0x0/0x8
Reported-by: Tim van der Staaij <[email protected]>
Signed-off-by: Sascha Hauer <[email protected]>
---
drivers/tty/serial/imx.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 13cb78340709a..83ea5b41930ab 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1457,8 +1457,10 @@ static int imx_uart_startup(struct uart_port *port)
imx_uart_writel(sport, ucr4 & ~UCR4_DREN, UCR4);
/* Can we enable the DMA support? */
- if (!uart_console(port) && imx_uart_dma_init(sport) == 0)
+ if (!uart_console(port) && imx_uart_dma_init(sport) == 0) {
+ lockdep_set_subclass(&port->lock, 1);
dma_is_inited = 1;
+ }
spin_lock_irqsave(&sport->port.lock, flags);
--
2.39.2