Date: Sat, 4 Apr 2009 22:23:03 +0000 (UTC) From: Marcel Moolenaar <marcel@FreeBSD.org> To: cvs-src-old@freebsd.org Subject: cvs commit: src/sys/powerpc/aim swtch.S Message-ID: <200904042223.n34MNFK5035138@repoman.freebsd.org>
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marcel 2009-04-04 22:23:03 UTC
FreeBSD src repository
Modified files:
sys/powerpc/aim swtch.S
Log:
SVN rev 190704 on 2009-04-04 22:23:03Z by marcel
Perform a dummy stwcx. when we switch contexts. The context
being switched out may hold a reservation. The stwcx. will
clear the reservation. This is architecturally recommended.
The scenario this addresses is as follows:
1. Thread 1 performs a lwarx and as such holds a reservation.
2. Thread 1 gets switched out (before doing the matching
stwcx.) and thread 2 is switched in.
3. Thread 2 performs a stwcx. to the same reservation granule.
This will succeed because the processor has the reservation
even though thread 2 didn't do the lwarx.
Note that on some processors the address given the stwcx. is
not checked. On these processors the mere condition of having
a reservation would cause the stwcx. to succeed, irrespective
of whether the addresses are the same. The dummy stwcx. is
especially important for those processors.
Revision Changes Path
1.28 +6 -0 src/sys/powerpc/aim/swtch.S
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