> On 13 Jun 2017, at 19:53, Zbigniew Bodek <[email protected]> wrote:
>
> Author: zbb
> Date: Tue Jun 13 18:53:56 2017
> New Revision: 319913
> URL: https://svnweb.freebsd.org/changeset/base/319913
>
> Log:
> Fix INVARIANTS debug code in HWPMC
>
> When HWPMC stops sampling, ps_pmc may be freed before samples
> are processed. In such situation treat PMC as stopped.
What is the sequence leading up to this?
...
> Modified: head/sys/dev/hwpmc/hwpmc_mod.c
> ==============================================================================
> --- head/sys/dev/hwpmc/hwpmc_mod.c Tue Jun 13 18:52:39 2017
> (r319912)
> +++ head/sys/dev/hwpmc/hwpmc_mod.c Tue Jun 13 18:53:56 2017
> (r319913)
> @@ -4224,7 +4224,8 @@ pmc_capture_user_callchain(int cpu, int ring, struct t
> ps_end = psb->ps_write;
> do {
> #ifdef INVARIANTS
> - if (ps->ps_pmc->pm_state != PMC_STATE_RUNNING)
> + if ((ps->ps_pmc == NULL) ||
> + (ps->ps_pmc->pm_state != PMC_STATE_RUNNING))
Isn’t this just moving the NULL pointer dereference later in the function? I’m
interested in knowing how the NULL pointer got into this function.
> nfree++;
> #endif
> if (ps->ps_nsamples != PMC_SAMPLE_INUSE)
> @@ -4262,9 +4263,11 @@ next:
> ps = psb->ps_samples;
> } while (ps != ps_end);
>
> +#ifdef INVARIANTS
> KASSERT(ncallchains > 0 || nfree > 0,
> ("[pmc,%d] cpu %d didn't find a sample to collect", __LINE__,
> cpu));
> +#endif
Why is this needed? KASSERT is a top when INVARIANTS is undefined.
Andrew
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