svn commit: r311287 - head/lib/libc/x86/sys

[Ngie Cooper (yaneurabeya)]

> On Jan 4, 2017, at 08:10, Konstantin Belousov <kib at freebsd.org> wrote:
> 
> Author: kib
> Date: Wed Jan  4 16:10:52 2017
> New Revision: 311287
> URL: https://svnweb.freebsd.org/changeset/base/311287
> 
> Log:
>  __vdso_gettc(): be extra careful with /dev/hpet mappings, never unmap
>  the mapping which might be accessed by other threads.
> 
>  If a pointer to the /dev/hpet register page mapping was stored into
>  the hpet_dev_map, other threads might access the page at any time.
>  Never unmap it, instead, keep track of mappings for all hpet units in
>  smal array.  Store pointer to the newly mapped registers page using
>  CAS, to detect parallel mappings.
> 
>  It appeared relatively easy to demonstrate the problem by arranging
>  two threads which perform gettimeofday(2) concurently, first time in
>  the process address space, when HPET is used for timecounter.
> 
>  PR:	215715
>  Sponsored by:	The FreeBSD Foundation
>  MFC after:	1 week

Thank you very much for the work! I’ll try to reproduce the bug again with the ATF test.
-Ngie
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