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author | Yang Xiaowei <xiaowei.yang@intel.com> | 2009-09-09 12:44:52 -0700 |
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committer | Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> | 2009-09-09 16:38:44 -0700 |
commit | 2496afbf1e50c70f80992656bcb730c8583ddac3 (patch) | |
tree | fd701f588d8194cb1b296eca9c6288b6b8c342a1 /arch | |
parent | 4d576b57b50a92801e6493e76e5243d6cff193d2 (diff) | |
download | kernel_samsung_smdk4412-2496afbf1e50c70f80992656bcb730c8583ddac3.zip kernel_samsung_smdk4412-2496afbf1e50c70f80992656bcb730c8583ddac3.tar.gz kernel_samsung_smdk4412-2496afbf1e50c70f80992656bcb730c8583ddac3.tar.bz2 |
xen: use stronger barrier after unlocking lock
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>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/x86/xen/spinlock.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 2f91e56..36a5141 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -326,8 +326,13 @@ static void xen_spin_unlock(struct raw_spinlock *lock) smp_wmb(); /* make sure no writes get moved after unlock */ xl->lock = 0; /* release lock */ - /* make sure unlock happens before kick */ - barrier(); + /* + * Make sure unlock happens before checking for waiting + * spinners. We need a strong barrier to enforce the + * write-read ordering to different memory locations, as the + * CPU makes no implied guarantees about their ordering. + */ + mb(); if (unlikely(xl->spinners)) xen_spin_unlock_slow(xl); |