Messages in this thread | | | Date | Wed, 18 Mar 2015 14:59:10 +0100 | From | Quentin Lambert <> | Subject | Re: [PATCH v2] Staging: dgnc: release the lock before testing for nullity |
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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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