linux-kernel - perf: multiple mmap of fd behavior on x86/ARM

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Message-ID: <alpine.DEB.2.20.1708101448460.30979@macbook-air>
Date:   Thu, 10 Aug 2017 14:48:52 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     linux-kernel@...r.kernel.org
cc:     Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: perf: multiple mmap of fd behavior on x86/ARM


So I was working on my perf_event_tests on ARM/ARM64 (the end goal was to 
get ARM64 rdpmc support working, but apparently those patches never made 
it upstream?)

anyway one test was failing due to an x86/arm difference, which is 
possibly only tangentially perf related.

On x86 you can mmap() a perf_event_open() file descriptor multiple times 
and it works.

On ARM/ARM64 you can only mmap() it once, any other attempts fail.

Is this expected behavior?

You can run the
	tests/record_sample/mmap_multiple
test in the current git of my perf_event_tests testsuite for a testcase.

Vince