Re: [PATCH 0/2] Triggering a softlockup panic during SMP boot

[Luis Chamberlain]

On Fri, Oct 27, 2023 at 02:46:26PM -0700, Krister Johansen wrote:
> Hi,
> This pair of patches was the result of an unsuccessful attempt to set
> softlockup_panic before SMP boot.  The rationale for wanting to set this
> parameter is that some of the VMs that my team runs will occasionally
> get stuck while onlining the non-boot processors as part of SMP boot.
> 
> In the cases where this happens, we find out about it after the instance
> successfully boots; however, the machines can get stuck for tens of
> minutes at a time before finally completing onlining processors.  Since
> we pay per minute for many of these VMs there were two goals for setting
> this value on boot: first, fail fast and hope that a subsequent boot
> attempt will be successful.  Second, a panic is a little easier to keep
> track of, especially if we're scraping serial logs after the fact.  In
> essence, the goal is to trigger the failure earlier and hopefully get
> more useful information for further debugging the problem as well.
> 
> While testing to make sure that this value was getting correctly set on
> boot, I ran into a pair of surprises.  First, when the softlockup_panic
> parameter was migrated to a sysctl alias, it had the side effect of
> setting the parameter value after SMP boot has occurred, when it used to
> be set before this.  Second, testing revealed that even though the
> aliases were being correctly processed, the kernel was reporting the
> commandline arguments as unrecognized. This generated a message in the
> logs about an unrecognized parameter (even though it was) and the
> parameter was passed as an environment variable to init.
> 
> The first patch ensures that aliased sysctl arguments are not reported
> as unrecognized boot arguments.
> 
> The second patch moves the setting of softlockup_panic earlier in boot,
> where it can take effect before SMP boot beings.

Thanks! Looks good, merged and will push to Linus soon.

  Luis