TTY 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. E.g.
ioctl()
tty_ioctl()
spin_lock(&tty_port->lock)
printk()
call_console_drivers()
foo_console_write()
spin_lock(&uart_port->lock)
tty_wakeup()
spin_lock(&tty_port->lock) << deadlock
This patch adds tty_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:
ioctl()
tty_ioctl()
printk_safe_enter()
spin_lock(&tty_port->lock)
printk()
printk_safe_log_store()
irq_work_queue()
spin_unlock(&tty_port->lock)
printk_safe_exit()
IRQ
printk_safe_flush_buffer()
vprintk_deferred()
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
include/linux/tty.h | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/include/linux/tty.h b/include/linux/tty.h
index c56e3978b00f..828f91ab680b 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -252,6 +252,30 @@ struct tty_port {
void *client_data;
};
+#define tty_port_lock_irq(lock) \
+ do { \
+ printk_safe_enter_irq(); \
+ spin_lock(lock); \
+ } while (0)
+
+#define tty_port_unlock_irq(lock) \
+ do { \
+ spin_unlock(lock); \
+ printk_safe_exit_irq(); \
+ } while (0)
+
+#define tty_port_lock_irqsave(lock, flags) \
+ do { \
+ printk_safe_enter_irqsave(flags); \
+ spin_lock(lock); \
+ } while (0)
+
+#define tty_port_unlock_irqrestore(lock, flags) \
+ do { \
+ spin_unlock(lock); \
+ printk_safe_exit_irqrestore(flags); \
+ } while (0)
+
/* tty_port::iflags bits -- use atomic bit ops */
#define TTY_PORT_INITIALIZED 0 /* device is initialized */
#define TTY_PORT_SUSPENDED 1 /* device is suspended */
--
2.17.1
--
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