On Fri, Nov 09, 2007 at 04:08:06PM -0600, Becky Bruce wrote: > The context switch code in the kernel issues a dummy stwcx. to clear the > reservation, as recommended by the architecture. However, some processors > can have issues if this stwcx to address A occurs while the reservation > is already held to a different address B. To avoid this problem, the dummy > stwcx. needs to be paired with a dummy lwarx to the same address. > > This patch adds the dummy lwarx, and creates a cpu feature bit to indicate > which cpus are affected. Tested on mpc8641_hpcn_defconfig in arch/powerpc; > build tested in arch/ppc.
You're still exposed even with this patch. The stwcx is there to protect from the cases where process 1 does lwarx and get context switched out to process 2 that by pure random chance does a stwcx. to the same reservation granule and succeeds, in spite of not having done the lwarx (on this side of the context switch). In exactly that case, process 2 will instead of doing a store to a reservation it didn't take on it's own, do a dangling stwcx, which is your erratum. Right? Seems like a "better" (but still ugly) workaround would be to create a _new_ reservation to a RA that's unavailable to any userspace process, so that they could never do a successful store to it. That way you would have stray reservations, but never dangling stwcx:es. No? -Olof _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
