Re: [PATCH -next 2/3] md/raid10: convert resync_lock to use seqlock

[Guoqing Jiang]

On 9/2/22 8:56 AM, Logan Gunthorpe wrote:
> On 2022-09-01 18:49, Guoqing Jiang wrote:
> > On 9/2/22 2:41 AM, Logan Gunthorpe wrote:
> > > Hi,
> > >
> > > On 2022-08-29 07:15, Yu Kuai wrote:
> > > > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> > > >
> > > > Currently, wait_barrier() will hold 'resync_lock' to read
> > > > 'conf->barrier',
> > > > and io can't be dispatched until 'barrier' is dropped.
> > > >
> > > > Since holding the 'barrier' is not common, convert 'resync_lock' to use
> > > > seqlock so that holding lock can be avoided in fast path.
> > > >
> > > > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > > I've found some lockdep issues starting with this patch in md-next while
> > > running mdadm tests (specifically 00raid10 when run about 10 times in a
> > > row).
> > >
> > > I've seen a couple different lock dep errors. The first seems to be
> > > reproducible on this patch, then it possibly changes to the second on
> > > subsequent patches. Not sure exactly.
> > That's why I said "try mdadm test suites too to avoid regression." ...
> You may have to run it multiple times, a single run tends not to catch
> all errors. I had to loop the noted test 10 times to be sure I hit this
> every time when I did the simple bisect.
>
> And ensure that all the debug options are on when you run it (take a
> look at the Kernel Hacking section in menuconfig). You won't hit this
> bug without at least CONFIG_PROVE_LOCKING=y.

Yes,  we definitely need to enable the option to test change for locking 
stuffs.

Thanks,
Guoqing