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

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Message-ID: <YbHBb2uB9JRP0tWc@kroah.com>
Date:   Thu, 9 Dec 2021 09:42:23 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     wigin zeng <wigin.zeng@....com>
Cc:     "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: 答复: [PATCH] serial: 8250: add
 lock for dma rx

A: http://en.wikipedia.org/wiki/Top_post
Q: Were do I find info about this thing called top-posting?
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

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