[PATCH] powerpc/fadump: re-register firmware-assisted dump if already registered

[Petr Tesarik]

On Fri, 14 Sep 2018 19:36:02 +0530
Hari Bathini <hbathini at linux.ibm.com> wrote:

> Firmware-Assisted Dump (FADump) needs to be registered again after any
> memory hot add/remove operation to update the crash memory ranges. But
> currently, the kernel returns '-EEXIST' if we try to register without
> uregistering it first. This could expose the system to racing issues
> while unregistering and registering FADump from userspace during udev
> events. Spare the userspace of this and let it be taken care of in the
> kernel space for a simpler interface.
> 
> Since this change, running 'echo 1 > /sys/kernel/fadump_registered'
> would result in re-regisering (unregistering and registering) FADump,
> if it was already registered.

Great improvement to the API!

Any suggestions what should be done in a client which tries to be
compatible with kernels before this change and after this change?

Petr T

> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
> ---
>  arch/powerpc/kernel/fadump.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index a711d22..761b28b 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -1444,8 +1444,8 @@ static ssize_t fadump_register_store(struct kobject *kobj,
>  		break;
>  	case 1:
>  		if (fw_dump.dump_registered == 1) {
> -			ret = -EEXIST;
> -			goto unlock_out;
> +			/* Un-register Firmware-assisted dump */
> +			fadump_unregister_dump(&fdm);
>  		}
>  		/* Register Firmware-assisted dump */
>  		ret = register_fadump();
>