Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH v3.4-rc5] block: iocontext->nr_tasks should be initialized to one | Date | Tue, 01 May 2012 14:31:07 -0400 |
| |
Jens Axboe <jaxboe@fusionio.com> writes:
> On 2012-05-01 20:09, Tejun Heo wrote: >> On Tue, May 01, 2012 at 08:02:39PM +0200, Jens Axboe wrote: >>> On 2012-05-01 18:17, Tejun Heo wrote: >>>> create_task_io_context() left ioc->nr_tasks at zero; however, a newly >>>> created ioc should have its nr_tasks initialized to one as it begins >>>> attached to the task creating it. >>>> >>>> This affects only CLONE_IO which currently doesn't seem to have any >>>> actual user. Sasha triggered WARN_ON_ONCE() in ioc_task_link() using >>>> syscall fuzzer. Even when it happens, the failure mode isn't critical >>>> (blk-cgroup may allow attaching a CLONE_IO'd task to a cgroup when it >>>> shouldn't and blkcg limits may behave weirdly). >>> >>> CLONE_IO is an exported interface, it can be set from clone(2). >>> Otherwise Sasha would not have hit this :-) >> >> Yeah, but with pthread not exposing it, I'm very skeptical how much, >> if any, use it's getting. With its incompatibility with blk-cgroup >> and cfq being able to merge coop request streams, I'm not sure how >> much we need it. Maybe we can just make it noop? > > It's a lot more robust and specific than hoping to get coop merging. For > cfq, it also implies that multiple threads sharing an io context should > be accounted as one. > > But as to actual users, I really don't know. I agree it's probably not > that widely used. If google still had that code search, we could get a > better idea :-)
I know of one project: the venerable dump/restore utility uses CLONE_IO.
Cheers, Jeff
| |