Subject: [PATCH 1/2] tty: serial: msm: Fix sysrq spinlock recursion on non-DM

From: [email-masked] (Daniel Thompson)
Date: Thu, 30 Oct 2014 11:26:07 +0000

On 29/10/14 18:14, Stephen Boyd wrote:
> The handle_rx() path calls uart_handle_sysrq_char() with the port
> lock held. This causes a spinlock recursion. Release and
> reacquire the lock here to avoid this.
> 
> BUG: spinlock recursion on CPU#0, swapper/0
>  lock: msm_uart_ports+0x1e0/0x2d0, .magic: dead4ead, .owner: swapper/0, .owner_cpu: 0
> CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-rc7-00012-gb38ee8265941 #69
> [<c0013964>] (unwind_backtrace) from [<c0011f74>] (show_stack+0x10/0x14)
> [<c0011f74>] (show_stack) from [<c004ed1c>] (do_raw_spin_lock+0x11c/0x13c)
> [<c004ed1c>] (do_raw_spin_lock) from [<c02d44c0>] (msm_console_write+0x78/0x188)
> [<c02d44c0>] (msm_console_write) from [<c0052880>] (call_console_drivers.constprop.22+0xb4/0x144)
> [<c0052880>] (call_console_drivers.constprop.22) from [<c0053570>] (console_unlock+0x27c/0x4ac)
> [<c0053570>] (console_unlock) from [<c0053bb4>] (vprintk_emit+0x1f4/0x5a8)
> [<c0053bb4>] (vprintk_emit) from [<c04ad0ac>] (printk+0x30/0x40)
> [<c04ad0ac>] (printk) from [<c02c2990>] (__handle_sysrq+0x58/0x1b8)
> [<c02c2990>] (__handle_sysrq) from [<c02d41b0>] (msm_irq+0x694/0x6f8)
> [<c02d41b0>] (msm_irq) from [<c0055740>] (handle_irq_event_percpu+0x58/0x270)
> [<c0055740>] (handle_irq_event_percpu) from [<c0055994>] (handle_irq_event+0x3c/0x5c)
> [<c0055994>] (handle_irq_event) from [<c0057e84>] (handle_level_irq+0x9c/0x138)
> [<c0057e84>] (handle_level_irq) from [<c005509c>] (generic_handle_irq+0x24/0x38)
> [<c005509c>] (generic_handle_irq) from [<c000f730>] (handle_IRQ+0x44/0xb0)
> [<c000f730>] (handle_IRQ) from [<c0008518>] (msm_vic_handle_irq+0x44/0x64)
> [<c0008518>] (msm_vic_handle_irq) from [<c04b5ac4>] (__irq_svc+0x44/0x7c)
> Exception stack(0xc0719f68 to 0xc0719fb0)
> 9f60:                   00000001 00000001 00000000 c0722938 c0718000 c0769acc
> 9f80: 00000000 c0720098 c0769305 4117b362 c0769acc 00000000 01000000 c0719fb0
> 9fa0: c004cab0 c000f880 20000013 ffffffff
> [<c04b5ac4>] (__irq_svc) from [<c000f880>] (arch_cpu_idle+0x20/0x30)
> [<c000f880>] (arch_cpu_idle) from [<c004691c>] (cpu_startup_entry+0xf4/0x23c)
> [<c004691c>] (cpu_startup_entry) from [<c06d8b70>] (start_kernel+0x32c/0x394)
> 
> Cc: Frank Rowand <[email-masked]>
> Cc: Daniel Thompson <[email-masked]>
> Signed-off-by: Stephen Boyd <[email-masked]>
> ---
>  drivers/tty/serial/msm_serial.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index 4b6c78331a64..cedcc36762a2 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -174,6 +174,7 @@ static void handle_rx(struct uart_port *port)
>  	while ((sr = msm_read(port, UART_SR)) & UART_SR_RX_READY) {
>  		unsigned int c;
>  		char flag = TTY_NORMAL;
> +		int sysrq;
>  
>  		c = msm_read(port, UART_RF);
>  
> @@ -195,7 +196,10 @@ static void handle_rx(struct uart_port *port)
>  		else if (sr & UART_SR_PAR_FRAME_ERR)
>  			flag = TTY_FRAME;
>  
> -		if (!uart_handle_sysrq_char(port, c))
> +		spin_unlock(&port->lock);
> +		sysrq = uart_handle_sysrq_char(port, c);
> +		spin_lock(&port->lock);
> +		if (!sysrq)
>  			tty_insert_flip_char(tport, c, flag);

Does tty_insert_flip_char() need the port to be locked?