Re: [PATCH] fix: mdadm -Ss for external metadata don't stop container

[Neil Brown <neilb@suse.de>]

On Tue, 7 Dec 2010 06:44:21 +0000 "Hawrylewicz Czarnowski, Przemyslaw"
<przemyslaw.hawrylewicz.czarnowski@intel.com> wrote:

> Neil,
> 
> The one below is a fix for the problem we encounter quite often when we try to stop all arrays with mdadm -Ss. The main problem is that mdmon holds open container device and then exits. The time that system make clean up is quite long and mdadm invokes ARRAY_STOP ioctl when device is still opened. 
> Second resolution is to retry ioctl in mdadm after mdmon exits, but closing handle is I what should be done before process exist.
> Take a look at the patch below:
> 
> --
> Sometimes (~50%) mdadm -Ss cannot stop container as mdmon opens its device
> and do not close it before exit(). The period between open and release of
> handle is too long and md is not able stop device. Releasing handle before
> exit does not block md.
> 
> Signed-off-by: Przemyslaw Czarnowski <przemyslaw.hawrylewicz.czarnowski@intel.com>

I've applied this, but I'm not 100% sure it is completely safe.
mdmon holds the O_EXCL open to be sure that mdadm isn't creating or
assembling another array in the container.
mdadm will get an O_EXCL and then try sending a signal to mdmon.  If it
succeeds, it knows mdmon is still running.  But this patch might open a
window where mdadm can get O_EXCL, and a signal still works.

However I'm not certain that window wasn't already there, and this might just
make it a bit bigger.
I've put a note in my to-do list to look into this more closely and figure
out if there is a problem, and if so, how to fix it.

Thanks,
NeilBrown



> ---
>  monitor.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/monitor.c b/monitor.c
> index 59b4181..f166bc8 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -525,6 +525,7 @@ static int wait_and_act(struct supertype *container, int nowait)
>  				remove_pidfile(container->devname);
>  			exit_now = 1;
>  			signal_manager();
> +			close(fd);
>  			exit(0);
>  		}
>  	}