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* perf: bug in rdpmc/mmap accounting after exec
@ 2017-07-26 19:39 Vince Weaver
  2017-08-02 17:39 ` Peter Zijlstra
  0 siblings, 1 reply; 7+ messages in thread
From: Vince Weaver @ 2017-07-26 19:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Peter Zijlstra, Ingo Molnar,
	Arnaldo Carvalho de Melo, Stephane Eranian

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

^ permalink raw reply	[flat|nested] 7+ messages in thread

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Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-07-26 19:39 perf: bug in rdpmc/mmap accounting after exec Vince Weaver
2017-08-02 17:39 ` Peter Zijlstra
2017-08-03 18:04   ` Vince Weaver
2017-08-04  0:37   ` Andy Lutomirski
2017-08-04  9:17     ` Peter Zijlstra
2017-08-04 11:12       ` Peter Zijlstra
2017-08-10 12:01   ` [tip:perf/core] perf/x86: Fix RDPMC vs. mm_struct tracking tip-bot for Peter Zijlstra

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