Re: [PATCH 04/10] mdadm/Grow: sleep a while after removing disk in impose_level

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

On Tue, 3 Sep 2024 08:53:42 +0800
Xiao Ni <xni@redhat.com> wrote:

> On Mon, Sep 2, 2024 at 6:14 PM Mariusz Tkaczyk
> <mariusz.tkaczyk@linux.intel.com> wrote:
> >
> > On Wed, 28 Aug 2024 10:11:44 +0800
> > Xiao Ni <xni@redhat.com> wrote:
> >  
> > > It needs to remove disks when reshaping from raid456 to raid0. In
> > > kernel space it sets MD_RECOVERY_RUNNING. And it will fail to change
> > > level. So wait sometime to let md thread to clear this flag.
> > >
> > > This is found by test case 05r6tor0.
> > >
> > > Signed-off-by: Xiao Ni <xni@redhat.com>
> > > ---
> > >  Grow.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/Grow.c b/Grow.c
> > > index 2a7587315817..aaf349e9722f 100644
> > > --- a/Grow.c
> > > +++ b/Grow.c
> > > @@ -3028,6 +3028,12 @@ static int impose_level(int fd, int level, char
> > > *devname, int verbose) makedev(disk.major, disk.minor));
> > >                       hot_remove_disk(fd, makedev(disk.major, disk.minor),
> > > 1); }
> > > +             /*
> > > +              * hot_remove_disk lets kernel set MD_RECOVERY_RUNNING
> > > +              * and it can't set level. It needs to wait sometime
> > > +              * to let md thread to clear the flag.
> > > +              */
> > > +             sleep_for(5, 0, true);  
> >  
> 
> Hi Mariusz
> 
> > Shouldn't we check sysfs is shorter intervals? I know that is the simplest
> > way but big sleeps are generally not good.
> >
> > I will merge it if you don't want to rework it but you need to add log that
> > we are waiting 5 second for the user to not panic that it is frozen.  
> 
> Which sysfs do you mean? If we have a better way, I want to choose it.
> 

If we are sending hot remove to the disk, we can check if there is path
available: /sys/block/<mddev>/md/dev-{devnm}
if not, then device has been finally removed.
Eventually, we can see same in mdstat but checking path looks simpler to me.

Thanks,
Mariusz