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Message-ID: <alpine.DEB.2.20.1707261530320.3810@macbook-air>
Date:   Wed, 26 Jul 2017 15:39:01 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     linux-kernel@...r.kernel.org
cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Stephane Eranian <eranian@...il.com>
Subject: perf: bug in rdpmc/mmap accounting after exec

Hello

so one last bug found by the PAPI testsuite.

This one involves the rdpmc auto-disable on last unmap of an event 
feature.

Failing test case:

	fd=perf_event_open();
	addr=mmap(fd);
	exec()  // without closing or unmapping the event
	fd=perf_event_open();
	addr=mmap(fd);
	rdpmc()	// GPFs due to rdpmc being disabled

I won't pretend to be able to follow the rdpmc disabling code, but if I 
add some printks it looks like 
	current->mm->context.perf_rdpmc_allowed
isn't properly being reset on exec?

In fact, current->mm->context.perf_rdpmc_allowed goes negative which seems
like it shouldn't happen?

Anyway, a test case for this can be found in the perf_event_tests,
	tests/rdpmc/rdpmc_exec_papi

Vince

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