Peter Zijlstra <pet...@infradead.org> wrote:
> 019a316992ee ("rtnetlink: add reference counting to prevent module unload
> while dump is in progress")
>
> And that commit is _completely_ broken.
>
> 1) it not in fact a refcount, so using refcount_t is silly
Your suggestion is...?
> 2) there is a distinct lack of memory barriers, so we can easily
> observe the decrement while the msg_handler is still in progress.
I guess you mean it needs:
+ smp_mb__before_atomic();
refcount_dec(&rtnl_msg_handlers_ref[family]);
?
However, this refcount_dec is misplaced anyway as it would need
to occur from nlcb->done() (the handler function gets stored in socket for
use by next recvmsg), so this change is indeed not helpful at all.
> 3) waiting with a schedule()/yield() loop is complete crap and subject
> life-locks, imagine doing that rtnl_unregister_all() from a RT task.
Whats the alternative?
Only one I see is to pass THIS_MODULE to hook reg/unreg so we know what module
registered the
family for purpose of module get/put but thats going to be messy.
Alternatively we can of course sleep instead of schedule() but that
doesn't appear too appealing either (albeit it is a lot less intrusive).
Any other idea?
