linux-kernel - Re: ppc64le reliable stack unwinder and scheduled tasks

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Message-ID: <4b95b2f3-c5e8-4d21-88fe-9de6cd346954@redhat.com>
Date:   Mon, 14 Jan 2019 12:54:52 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Nicolai Stange <nstange@...e.de>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, live-patching@...r.kernel.org,
        Torsten Duwe <duwe@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Jiri Kosina <jkosina@...e.cz>,
        Balbir Singh <bsingharora@...il.com>
Subject: Re: ppc64le reliable stack unwinder and scheduled tasks

On 1/14/19 12:09 PM, Josh Poimboeuf wrote:
> On Mon, Jan 14, 2019 at 11:46:59AM -0500, Joe Lawrence wrote:
>> @@ -158,11 +158,21 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
>>   			return 1; /* invalid backlink, too far up. */
>>   		}
>>   
>> +		/* We can only trust the bottom frame's backlink, the rest
>> +		 * of the frame may be uninitialized, continue to the next. */
>> +		if (firstframe--)
>> +			goto next;
> 
> Won't this decrement firstframe on every iteration, so when firstframe
> is 0, it will decrement it to -1, causing it to 'goto next' on all
> future iterations?
> 

Argg, yes, that should be:

if (!firstframe) {
	firstframe = 0;
	goto next;
}

Apologies for the monday-morning crap-patch.

/runsoff to find some more caffeine

-- Joe