Re: [Lksctp-developers] [PATCH 1/3] sctp: fix autoclose timer race

[Vlad Yasevich <vladislav.yasevich@hp.com>]

Vlad Yasevich wrote:
> 
> Andrei Pelinescu-Onciul wrote:
>> For very small autoclose timeouts (e.g. 0 or close to 0 due to
>> overflows) it's possible that the timer is executed immediately
>> after is set, before there is a chance to increase the association
>> reference counter. To avoid this race, always reference the
>> association before calling mod_timer() and dereference it back if
>> the timer was already active.
>>
> 
> Actually, I don't think this can happen.  At worst, you'd trigger
> a soft lock-up, since the code modifying the timer is already holding
> a socket lock.  But that would only happen if that code is pre-empted,
> which would mean that a user version of the lock is held, then the
> autoclose would get rescheduled anyway.
> 

Even if the timer ends up running on a different CPU, the socket lock
guarantees that only 1 instance of the state machine is running per
socket.  The timer handler will spin on the lock until it's released,
so there doesn't appear to be a race.

-vlad