xen: use stronger barrier after unlocking lock

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We need to have a stronger barrier between releasing the lock and
checking for any waiting spinners.  A compiler barrier is not sufficient
because the CPU's ordering rules do not prevent the read xl->spinners
from happening before the unlock assignment, as they are different
memory locations.

We need to have an explicit barrier to enforce the write-read ordering
to different memory locations.

Because of it, I can't bring up > 4 HVM guests on one SMP machine.

[ Code and commit comments expanded -J ]

[ Impact: avoid deadlock when using Xen PV spinlocks ]

Signed-off-by: Yang Xiaowei <xiaowei.yang@intel.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

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Yang Xiaowei 2009-09-09 12:44:52 -07:00 • committed by Jeremy Fitzhardinge

parent 4d576b57b5

commit 2496afbf1e

1 changed files with 7 additions and 2 deletions

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arch/x86/xen/spinlock.c

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