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SubjectRe: [patch 1/2] raid6_end_write_request() spinlock fix
On Tue, Apr 25, 2006 at 04:50:10PM +1000, Neil Brown wrote:
> On Tuesday April 25, wrote:
> > On Tue, Apr 25, 2006 at 03:13:49PM +1000, Neil Brown wrote:
> > > On Tuesday April 25, wrote:
> > > > Hello,
> > > >
> > > > Reduce the raid6_end_write_request() spinlock window.
> > >
> > > Andrew: please don't include these in -mm. This one and the
> > > corresponding raid5 are wrong, and I'm not sure yet the unplug_device
> > > changes.
> >
> > I am sure with the unplug_device. Just look follow the path...
> >
> What path? There are probably several. If I follow the path, will I
> see the same things as you see? Who knows, because you haven't
> bothered to tell us what you see.

There are only two places where handle_list is possibly re-filled:
__release_stripe() and raidX_activate_delayed(). So raidXd should only
wakeup after these two points.

> >
> > Yes. Let's fix the error(). In any case, the current code is broken. (see raid5/6_end_read_request)
> What will I see in raidX_end_read_request. Surely it isn't that hard
> to write a few more sentences?

You should see md_error() in raidX_end_read_request isn't in any spinlocks.

> conf->working_disks isn't atomic_t and so decrementing without a
> spinlock isn't safe. So lets just leave it all inside a spinlock.

test_and_set_bit(Faulty, &rdev->flags) protects it as well imho.
It can be enter only once.

> Also I have a vague memory that clearing In_sync before Faulty is
> important, but I'm not certain of that.

Maybe, but seems not apply here.

> Remember: the code is there for a reason. It might not be a good
> reason, and the code could well be wrong. But it would be worth your
> effort trying to find out what the reason is before blithely changing
> it (as I discovered recently with a change I suggested to
> invalidate_mapping_pages).

Thanks :)
Coywolf Qi Hunt
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