Subject: Re: powerpc/xmon: Fix invocation inside lock region

From: Michael Ellerman <[email-masked]>
Date: Sat, 8 Dec 2018 00:07:01 +1100 (AEDT)

On Thu, 2018-11-08 at 17:12:42 UTC, Breno Leitao wrote:
> Currently xmon needs to get devtree_lock (through rtas_token()) during its
> invocation (at crash time). If there is a crash while devtree_lock is being
> held, then xmon tries to get the lock but spins forever and never get into
> the interactive debugger, as in the following case:
> 
> 	int *ptr = NULL;
> 	raw_spin_lock_irqsave(&devtree_lock, flags);
> 	*ptr = 0xdeadbeef;
> 
> This patch avoids calling rtas_token(), thus trying to get the same lock,
> at crash time. This new mechanism proposes getting the token at
> initialization time (xmon_init()) and just consuming it at crash time.
> 
> This would allow xmon to be possible invoked independent of devtree_lock
> being held or not.
> 
> Signed-off-by: Breno Leitao <[email-masked]>
> Reviewed-by: Thiago Jung Bauermann <[email-masked]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/8d4a862276a9c30a269d368d324fb5

cheers