Re: [PATCH] Fix: Sometimes mdmon throws core dump during reshape

[NeilBrown <neilb@suse.de>]

On Mon, 05 Sep 2011 12:39:55 +0200 Adam Kwolek <adam.kwolek@intel.com> wrote:

> Problem was found during reshaping 2 volumes /raid0 and raid5/ in container.
> Sometimes mdmon throws core dump due to NULL pointer exception.
> 
> Problem occurs in scenario:
> - managemon: is about spare activation (degraded raid4 volume == raid0 under takeover)
> - managemon: detect level change and signals monitor (manage_member() calls replace_array())
> - monitor: detects transition raid4/5->raid0 and sets a->container to NULL
>            to indicate array deactivation
> - managemon : continues his work and tries to activate spare (a->check_degraded is set).
>               NULL pointer is passed to metadata handler activate_spare()
>               Core dump is generated.
> 
> To resolve this situation managemon (after monitor kick) checks again
> a->container pointer to learn if current array is not to be deactivated.

This looks like it might be the same bug as is fixed by
     Lukasz Dorau <lukasz.dorau@intel.com>
in
  Subject: [PATCH] FIX: Mdmon crashes after changing RAID level from 1 to 0

Does that look likely?

Thanks,
NeilBrown


> 
> Signed-off-by: Adam Kwolek <adam.kwolek@intel.com>
> ---
> 
>  managemon.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/managemon.c b/managemon.c
> index d020f82..3540dac 100644
> --- a/managemon.c
> +++ b/managemon.c
> @@ -475,6 +475,12 @@ static void manage_member(struct mdstat_ent *mdstat,
>  		}
>  	}
>  
> +	/* we are after monitor kick,
> +	 * so container field can be cleared - check it again
> +	 */
> +	if (a->container == NULL)
> +		return;
> +
>  	/* We don't check the array while any update is pending, as it
>  	 * might container a change (such as a spare assignment) which
>  	 * could affect our decisions.
> 
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