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

[Greg KH <gregkh@linuxfoundation.org>]

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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