Re: raid5d hangs when stopping an array during reshape

[Shaohua Li <shli@kernel.org>]

On Thu, Feb 25, 2016 at 11:31:04AM +1100, Neil Brown wrote:
> On Thu, Feb 25 2016, Shaohua Li wrote:
> 
> >
> > As for the bug, write requests run in raid5d, mddev_suspend() waits for all IO,
> > which waits for the write requests. So this is a clear deadlock. I think we
> > should delete the check_reshape() in md_check_recovery(). If we change
> > layout/disks/chunk_size, check_reshape() is already called. If we start an
> > array, the .run() already handles new layout. There is no point
> > md_check_recovery() check_reshape() again.
> 
> Are you sure?
> Did you look at the commit which added that code?
> commit b4c4c7b8095298ff4ce20b40bf180ada070812d0
> 
> When there is an IO error, reshape (or resync or recovery) will abort
> and then possibly be automatically restarted.

thanks pointing out this. 
> Without the check here a reshape might be attempted on an array which
> has failed.  Not sure if that would be harmful, but it would certainly
> be pointless.
> 
> But you are right that this is causing the problem.
> Maybe we should keep track of the size of the 'scribble' arrays and only
> call resize_chunks if the size needs to change?  Similar to what
> resize_stripes does.

yep, this is my first solution, but think check_reshape() is useless here
later, apparently miss the restart case. I'll go this way.

> It might also be good to put something like
>   WARN_ON(current == mddev->thread->task);
> in mddev_suspend() ... or whatever code would cause this sort of error
> to trigger a warning early.

Sounds good.

Thanks,
Shaohua