Re: [PATCH] uart:8250: change lock order in serial8250_do_startup()

From: Guenter Roeck
Date: Fri Aug 14 2020 - 10:09:54 EST

On 8/13/20 6:38 PM, Sergey Senozhatsky wrote:
> We have a number of "uart.port->desc.lock vs desc.lock->uart.port"
> lockdep reports coming from 8250 driver; this causes a bit of trouble
> to people, so let's fix it.
>
> The problem is reverse lock order in two different call paths:
>
> chain #1:
>
> serial8250_do_startup()
> spin_lock_irqsave(&port->lock);
> disable_irq_nosync(port->irq);
> raw_spin_lock_irqsave(&desc->lock)
>
> chain #2:
>
> __report_bad_irq()
> raw_spin_lock_irqsave(&desc->lock)
> for_each_action_of_desc()
> printk()
> spin_lock_irqsave(&port->lock);
>
> Fix this by changing the order of locks in serial8250_do_startup():
> do disable_irq_nosync() first, which grabs desc->lock, and grab
> uart->port after that, so that chain #1 and chain #2 have same lock
> order.
>
> Full lockdep splat:
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.4.39 #55 Not tainted
> ------------------------------------------------------
> swapper/0/0 is trying to acquire lock:
> ffffffffab65b6c0 (console_owner){-...}, at: console_lock_spinning_enable+0x31/0x57
>
> but task is already holding lock:
> ffff88810a8e34c0 (&irq_desc_lock_class){-.-.}, at: __report_bad_irq+0x5b/0xba
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #2 (&irq_desc_lock_class){-.-.}:
> _raw_spin_lock_irqsave+0x61/0x8d
> __irq_get_desc_lock+0x65/0x89
> __disable_irq_nosync+0x3b/0x93
> serial8250_do_startup+0x451/0x75c
> uart_startup+0x1b4/0x2ff
> uart_port_activate+0x73/0xa0
> tty_port_open+0xae/0x10a
> uart_open+0x1b/0x26
> tty_open+0x24d/0x3a0
> chrdev_open+0xd5/0x1cc
> do_dentry_open+0x299/0x3c8
> path_openat+0x434/0x1100
> do_filp_open+0x9b/0x10a
> do_sys_open+0x15f/0x3d7
> kernel_init_freeable+0x157/0x1dd
> kernel_init+0xe/0x105
> ret_from_fork+0x27/0x50
>
> -> #1 (&port_lock_key){-.-.}:
> _raw_spin_lock_irqsave+0x61/0x8d
> serial8250_console_write+0xa7/0x2a0
> console_unlock+0x3b7/0x528
> vprintk_emit+0x111/0x17f
> printk+0x59/0x73
> register_console+0x336/0x3a4
> uart_add_one_port+0x51b/0x5be
> serial8250_register_8250_port+0x454/0x55e
> dw8250_probe+0x4dc/0x5b9
> platform_drv_probe+0x67/0x8b
> really_probe+0x14a/0x422
> driver_probe_device+0x66/0x130
> device_driver_attach+0x42/0x5b
> __driver_attach+0xca/0x139
> bus_for_each_dev+0x97/0xc9
> bus_add_driver+0x12b/0x228
> driver_register+0x64/0xed
> do_one_initcall+0x20c/0x4a6
> do_initcall_level+0xb5/0xc5
> do_basic_setup+0x4c/0x58
> kernel_init_freeable+0x13f/0x1dd
> kernel_init+0xe/0x105
> ret_from_fork+0x27/0x50
>
> -> #0 (console_owner){-...}:
> __lock_acquire+0x118d/0x2714
> lock_acquire+0x203/0x258
> console_lock_spinning_enable+0x51/0x57
> console_unlock+0x25d/0x528
> vprintk_emit+0x111/0x17f
> printk+0x59/0x73
> __report_bad_irq+0xa3/0xba
> note_interrupt+0x19a/0x1d6
> handle_irq_event_percpu+0x57/0x79
> handle_irq_event+0x36/0x55
> handle_fasteoi_irq+0xc2/0x18a
> do_IRQ+0xb3/0x157
> ret_from_intr+0x0/0x1d
> cpuidle_enter_state+0x12f/0x1fd
> cpuidle_enter+0x2e/0x3d
> do_idle+0x1ce/0x2ce
> cpu_startup_entry+0x1d/0x1f
> start_kernel+0x406/0x46a
> secondary_startup_64+0xa4/0xb0
>
> other info that might help us debug this:
>
> Chain exists of:
> console_owner --> &port_lock_key --> &irq_desc_lock_class
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&irq_desc_lock_class);
> lock(&port_lock_key);
> lock(&irq_desc_lock_class);
> lock(console_owner);
>
> *** DEADLOCK ***
>
> 2 locks held by swapper/0/0:
> #0: ffff88810a8e34c0 (&irq_desc_lock_class){-.-.}, at: __report_bad_irq+0x5b/0xba
> #1: ffffffffab65b5c0 (console_lock){+.+.}, at: console_trylock_spinning+0x20/0x181
>
> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.39 #55
> Hardware name: XXXXXX
> Call Trace:
> <IRQ>
> dump_stack+0xbf/0x133
> ? print_circular_bug+0xd6/0xe9
> check_noncircular+0x1b9/0x1c3
> __lock_acquire+0x118d/0x2714
> lock_acquire+0x203/0x258
> ? console_lock_spinning_enable+0x31/0x57
> console_lock_spinning_enable+0x51/0x57
> ? console_lock_spinning_enable+0x31/0x57
> console_unlock+0x25d/0x528
> ? console_trylock+0x18/0x4e
> vprintk_emit+0x111/0x17f
> ? lock_acquire+0x203/0x258
> printk+0x59/0x73
> __report_bad_irq+0xa3/0xba
> note_interrupt+0x19a/0x1d6
> handle_irq_event_percpu+0x57/0x79
> handle_irq_event+0x36/0x55
> handle_fasteoi_irq+0xc2/0x18a
> do_IRQ+0xb3/0x157
> common_interrupt+0xf/0xf
> </IRQ>
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

> ---
> drivers/tty/serial/8250/8250_port.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 09475695effd..67f1a4f31093 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2275,6 +2275,11 @@ int serial8250_do_startup(struct uart_port *port)
>
> if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
> unsigned char iir1;
> + bool irq_shared = up->port.irqflags & IRQF_SHARED;
> +
> + if (irq_shared)
> + disable_irq_nosync(port->irq);
> +
> /*
> * Test for UARTs that do not reassert THRE when the
> * transmitter is idle and the interrupt has already
> @@ -2284,8 +2289,6 @@ int serial8250_do_startup(struct uart_port *port)
> * allow register changes to become visible.
> */
> spin_lock_irqsave(&port->lock, flags);
> - if (up->port.irqflags & IRQF_SHARED)
> - disable_irq_nosync(port->irq);
>
> wait_for_xmitr(up, UART_LSR_THRE);
> serial_port_out_sync(port, UART_IER, UART_IER_THRI);
> @@ -2297,9 +2300,9 @@ int serial8250_do_startup(struct uart_port *port)
> iir = serial_port_in(port, UART_IIR);
> serial_port_out(port, UART_IER, 0);
>
> - if (port->irqflags & IRQF_SHARED)
> - enable_irq(port->irq);
> spin_unlock_irqrestore(&port->lock, flags);
> + if (irq_shared)
> + enable_irq(port->irq);
>
> /*
> * If the interrupt is not reasserted, or we otherwise
>