UART port spin_lock is one of the locks that can cause a
printk-recursion deadlock, thus we need to lock it from
printk_safe context. An example of a possible deadlock:
IRQ
foo_console_handle_IRQ()
spin_lock(&uart_port->lock)
tty_wakeup()
printk()
call_console_drivers()
foo_console_write()
spin_lock(&uart_port->lock) << deadlock
This patch adds uart_port->lock helper macros which take care
of printk_safe context and redirect potentially unsafe printk()
calls to per-CPU buffers, which we flush later from safe a
context. The helper macros will turn the above mentioned deadlock
scenario into:
IRQ
foo_console_handle_IRQ()
printk_safe_enter()
spin_lock(&uart_port->lock)
tty_wakeup()
printk()
printk_safe_log_store()
irq_work_queue()
spin_unlock(&uart_port->lock)
printk_safe_exit()
iret
IRQ
printk_safe_flush_buffer()
vprintk_deferred()
Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
---
include/linux/serial_core.h | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 06ea4eeb09ab..deb464520946 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -256,6 +256,41 @@ struct uart_port {
void *private_data; /* generic platform
data pointer */
};
+#define uart_port_lock_irq(lock) \
+ do { \
+ printk_safe_enter_irq(); \
+ spin_lock(lock); \
+ } while (0)
+
+#define uart_port_unlock_irq(lock) \
+ do { \
+ spin_unlock(lock); \
+ printk_safe_exit_irq(); \
+ } while (0)
+
+#define uart_port_lock_irqsave(lock, flags) \
+ do { \
+ printk_safe_enter_irqsave(flags); \
+ spin_lock(lock); \
+ } while (0)
+
+#define uart_port_trylock_irqsave(lock, flags) \
+ ({ \
+ int locked; \
+ \
+ printk_safe_enter_irqsave(flags); \
+ locked = spin_trylock(lock); \
+ if (!locked) \
+ printk_safe_exit_irqrestore(flags); \
+ locked; \
+ })
+
+#define uart_port_unlock_irqrestore(lock, flags) \
+ do { \
+ spin_unlock(lock); \
+ printk_safe_exit_irqrestore(flags); \
+ } while (0)
+
static inline int serial_port_in(struct uart_port *up, int offset)
{
return up->serial_in(up, offset);
--
2.17.1
