On 05/17/2012 02:18 PM, KAMEZAWA Hiroyuki wrote:
(2012/05/17 18:52), Glauber Costa wrote:
On 05/17/2012 09:37 AM, Andrew Morton wrote:
If that happens, locking in static_key_slow_inc will prevent any damage.
My previous version had explicit code to prevent that, but we were
pointed out that this is already part of the static_key expectations, so
that was dropped.
This makes no sense. If two threads run that code concurrently,
key->enabled gets incremented twice. Nobody anywhere has a record that
this happened so it cannot be undone. key->enabled is now in an
unknown state.
Kame, Tejun,
Andrew is right. It seems we will need that mutex after all. Just this
is not a race, and neither something that should belong in the
static_branch interface.
Hmm....how about having
res_counter_xchg_limit(res,&old_limit, new_limit);
if (!cg_proto->updated&& old_limit == RESOURCE_MAX)
....update labels...
Then, no mutex overhead maybe and activated will be updated only once.
Ah, but please fix in a way you like. Above is an example.
I think a mutex is a lot cleaner than adding a new function to the
res_counter interface.
We could do a counter, and then later decrement the key until the
counter reaches zero, but between those two, I still think a mutex here
is preferable.
Only that, instead of coming up with a mutex of ours, we could export
and reuse set_limit_mutex from memcontrol.c
Thanks,
-Kame
(*) I'm sorry I won't be able to read e-mails, tomorrow.
Ok Kame. I am not in a terrible hurry to fix this, it doesn't seem to be
hurting any real workload.
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