linux-kernel - Re: [BUG]: 2.6.19.2: Weird serial core issue

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Message-ID: <20070201111618.GA3462@flint.arm.linux.org.uk>
Date:	Thu, 1 Feb 2007 11:16:18 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Aubrey Li <aubreylee@...il.com>
Cc:	Alan <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [BUG]: 2.6.19.2: Weird serial core issue

On Thu, Feb 01, 2007 at 06:09:24PM +0800, Aubrey Li wrote:
> On 2/1/07, Russell King <rmk+lkml@....linux.org.uk> wrote:
> >On Thu, Feb 01, 2007 at 10:33:40AM +0800, Aubrey Li wrote:
> >> On 2/1/07, Alan <alan@...rguk.ukuu.org.uk> wrote:
> >> >What code is running on that console at the time. Most likely that user
> >> >code is also saving/restoring terminal settings so overwrite yours
> >> >
> >>
> >> I implemented the serial driver by myself, :). See the attachment.
> >> I didn't save/restore terminal setting in the my_set_termios().
> >>
> >> I trace this back till tty_tioctl(..., unsigned long arg), everytime I
> >> type "ENTER" key,
> >> the argument "arg" passed into tty_ioctl() is the address of a termios
> >> structure, which include wrong c_cflag.
> >
> >If userspace is issuing an ioctl to re-enable crtscts, and the kernel
> >is obliging, how can this be a kernel bug?
> 
> But the fact is not.
> 1) kernel boot up and enable crtscts by default
> 2) issue an ioctl to disable crtscts.
> 3) not do anything but type "ENTER", kernel re-enable crtscts.
> 
> That's wrong. Terminal setting seems not be recorded by the serial core.

serial core does not and should not "record" the terminal settings.
That's the job of the tty layer.

> Is it clear?

No.  You haven't analysed the call path causing tty_ioctl() to be
invoked, so you have no basis to point the finger *anywhere* at the
moment.

Find out from where tty_ioctl() is called - maybe by adding a call
to dump_stack().  I think you'll find it is coming from userspace.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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