On 18/03/2015 14:54, Dan Carpenter wrote:
On Wed, Mar 18, 2015 at 02:43:01PM +0100, Quentin Lambert wrote:
On 18/03/2015 14:36, Dan Carpenter wrote:
This changelog still doesn't make sense so I took a look at the code.
tty_ldisc_deref() is an unlock function. So this is a lock ordering
bug. What makes you think the original ordering was correct? Who
reported this bug? What are the effects of this bug?
I was the one who introduced the ordering change in the first place.
I am just trying to fix it because although nobody complained I am not
sure of the impact and restoring the previous control flow seems to be the
right thing to do.
Your changelog should tell me this stuff.
Should I send a third version then?
The original code is wrong. We take "spin_lock_irqsave(&ch->ch_lock,
flags);" before we do "ld = tty_ldisc_ref(tp);" so we should deref
before we unlock.
It's normally:
lock_outer();
lock_inner();
unlock_inner();
unlock_outer();
On the success path we unlock first then deref and that is a mistake.
I didn't know that thank you.
This kind of change is a bit dangerous though so it requires testing.
Ok, should I act on that? What do you advice?
regards,
dan carpenter
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