Re: [tipc-discussion] [PATCH net-next v3 01/12] tipc: convert 'blocked' flag in struct tipc_bearer to atomic_t

[Erik H. <eri...@er...>]

On Mon, Sep 30, 2013 at 04:38:13PM +0800, Ying Xue wrote:
> The 'blocked' flag in struct tipc_bearer is currently protected by
> a big spinlock aggregated into tipc_bearer. We want to reduce all
> dependencies to this lock, as part of our effort to make the locking
> policy simpler and more manageable.
> 
> Furthermore, the functions tipc_disc_recv_msg() and disc_send_msg()
> access the flag without taking this lock at all, implying a risk that
> they may occasionally obtain a wrong value and drop sending/receiving
> of discovery messages. Since discovery messages are timer driven and
> best-effort, the latter problem is not fatal, but it is clearly avoidable.
> 
> By converting the type of the flag from int to atomic_t we eliminate
> both the spinlock dependency and the current race condition.
> 
> We also make two small code changes:
> 
> 1) The functions tipc_continue() and bearer_blocked() now become
>    one-liners doing a single access to the flag. So we just remove
>    those redundant functions.
> 
> 2) The initialization of the flag is moved from the enable_media()
>    functions in ib_media.c and eth_media.c respecively, to the generic
>    tipc_enable_bearer() function, so that it is done in one place only.
> 
> Signed-off-by: Ying Xue <yin...@wi...>

Also, recent findings (off-list discussion) that we disobey the locking rules
of del_timer_sync by holding the same spinlock in the timer handler
as when we delete the timer, leading to deadlocks during bearer disable..

Acked-by: Erik Hugne <eri...@er...>