Date: Wed, 14 Jun 2017 00:32:21 +0100 From: Andrew Turner <andrew@fubar.geek.nz> To: Zbigniew Bodek <zbb@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r319913 - head/sys/dev/hwpmc Message-ID: <8886277B-6036-41E8-819D-47AD6990F019@fubar.geek.nz> In-Reply-To: <201706131853.v5DIruKH034954@repo.freebsd.org> References: <201706131853.v5DIruKH034954@repo.freebsd.org>
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> On 13 Jun 2017, at 19:53, Zbigniew Bodek <zbb@freebsd.org> 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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