Re: tty_flip_buffer() from atomic context when low_latency==1

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2011-08-19, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

>> But, many drivers appear to call tty_flip_buffer_push() from an atomic
>> context. If that is done with tty->low_latency==1 it turns into a call
>> to flush_to_ldisc(), which then calls disc->ops->receive_buf(), which
>> must not be called from an atomic context.
>
> It's covered under "So don't do that then".

I don't do that, and wasn't asking if I should.

My point was that most of the drivers in the linux kernels sources
_do_ appear to do that, and I don't see how they avoid problems.

For exaple, 8250.c calls tty_flip_buffer_push() from receive_chars(),
calld from serial8250_handle_port(), called from
serial8250_interrupt().

How are problems avoided when tty->low_latency is set?

Is tty->low_latency never allowed to be set for the 8250 driver?

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