On 1/5/2018 7:06 PM, Alan Cox wrote:
On Fri, 5 Jan 2018 13:15:45 +0530
"Kohli, Gaurav" <gkohli@xxxxxxxxxxxxxx> wrote:
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.
Which is fine.
If the flush_to_ldisc gets there first then it will find there is a NULL
ldisc and do nothing. When it finishes the tty_init_dev will run and will
be protected from a further re-entry.
If the init_dev gets there first it will complete the init before the
flush_to_ldisc is permitted to proceed.
In other words we restore the intended invariant that ldisc's do not get
entered while their setup routine is running.
But in above case , there we can hit another race, if we have a sequence
like this
tty_init_dev->alloc_tty_struct -> tty_ldisc_init -> this will initialize
ldisc ,
but at this moment disc_data is still NULL
And if flush_to_ldisc comes in between, it will take ldisc reference and
proceeds receive buffer.
Regards
Gaurav
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