答复: 答复: [PATCH] serial: 8250: add lock for dma rx

[wigin zeng]

> What issue exactly?
The interval of UART input packages is very small(1ms~ 10ms), and some package size larger than configured DMA transfer size.

> But what data is being accessed at the same time to cause a crash?
> How is data being added into the buffer at the same time in two different places into the same queue?  What userspace programs are causing this?
Both places will modify tty_port *port->buf.tail (kmalloc operation and write the data/flag into this address)

>So all tty buffer accesses need to be protected by your new lock?
New lock only protected the tty_buffer alloc and write operation in serial-tty case. 

BRs
Wigin
-----邮件原件-----
发件人: Greg KH [mailto:gregkh@xxxxxxxxxxxxxxxxxxx] 
发送时间: 2021年12月9日 16:42
收件人: wigin zeng <wigin.zeng@xxxxxxx>
抄送: jirislaby@xxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
主题: Re: 答复: [PATCH] serial: 8250: add lock for dma rx

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On Thu, Dec 09, 2021 at 08:15:00AM +0000, wigin zeng wrote:
> We encountered this issue when UART transfer very intensive.

What issue exactly?

> DMA irq-thread processed on CPU0 and serial irq-thread executing on 
> CPU1, In DMA irq-thread will invoke "tty_insert_filp_string" function to add the rx_buf into tty_buffer.
> In serial irq-thread also has chance to access tty_insert_flip_char(in serial8250_rx_chars ) to access tty_buffer.
> there is race condition, sometimes will cause panic.

But what data is being accessed at the same time to cause a crash?
How is data being added into the buffer at the same time in two different places into the same queue?  What userspace programs are causing this?

> We add the spin_lock to sync the tty_buffer operation, and the issue gone after applied the patch.

So all tty buffer accesses need to be protected by your new lock?

thanks,

greg k-h
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