Re: Crash in elevator_dispatch_fn() (e.g. deadline_dispatch()) whenchanging elevators.

From: Frank Mayhar
Date: Thu Jan 23 2014 - 13:38:43 EST

On Wed, 2014-01-22 at 07:46 -0800, Frank Mayhar wrote:
> On Tue, 2014-01-21 at 07:58 -0800, Frank Mayhar wrote:
> > Replacing? Or adding to? Is BYPASS always set when DYING is set? (My
> > guess is not but I haven't done an exhaustive analysis.) So the
> > relevant code snippet in __elv_next_request() would be:
> > if (unlikely(blk_queue_dying(q)) ||
> > unlikely(blk_queue_bypass(q)) ||
> > !q->elevator->type->ops.elevator_dispatch_fn(q, 0))
> > return NULL;
> FYI, I've made this change and tested it. I can't say for certain that
> it fixes the crash (since it's one of those races that's difficult to
> reproduce), but it does seem to pass all the tests I've thrown at it so
> far.

Um, does anyone care about this? Tejun? Jens? Anyone?

This is a real crash; it would be nice if someone would weigh in.
Frank Mayhar

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