linux-kernel - Re: [PATCH] tty: fix data race in n_tty_receive_buf

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Date:   Fri, 5 Jan 2018 13:15:45 +0530
From:   "Kohli, Gaurav" <gkohli@...eaurora.org>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     jslaby@...e.com, gregkh@...uxfoundation.org, mikey@...ling.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] tty: fix data race in n_tty_receive_buf_common

Hi Alan,
>>>
>>> Can you make that code available otherwise it's impossible to see 
>>> what the problem might be.
>
>
  https://source.codeaurora.org/quic/la/kernel/msm-4.9/tree/drivers/tty/serial?h=msm-4.9
  As discussed , there not seems a problem as we are getting print 
request even when port seems to closed.


tty_ldisc_lock(tty, 5 * HZ);
  tty_ldisc_setup(tty);
  tty_ldisc_unlock(tty)

But in above lock,  there is a chance when flush_to_ldisc will occur 
first and acquired a lock in
tty_ldisc_ref itself.
So this may fail, I am not much sure here, Please correct me, If i am 
missing something here.
> So can not we simply return from flush_to_ldisc ,when we know 
> disc_data is not valid like
> we are doing for tty and ldisc already?
>
> if (tty->disc_data == NULL) {
>                 tty_ldisc_deref(disc);
>                 return;
>         }
>
>
>
>


Regards
Gaurav
-- Qualcomm India Private Limited, on behalf of Qualcomm Innovation 
Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation 
Collaborative Project.