[SPARC64]: Avoid membar instructions in delay slots.

In particular, avoid membar instructions in the delay
slot of a jmpl instruction.

UltraSPARC-I, II, IIi, and IIe have a bug, documented in
the UltraSPARC-IIi User's Manual, Appendix K, Erratum 51

The long and short of it is that if the IMU unit misses
on a branch or jmpl, and there is a store buffer synchronizing
membar in the delay slot, the chip can stop fetching instructions.

If interrupts are enabled or some other trap is enabled, the
chip will unwedge itself, but performance will suffer.

We already had a workaround for this bug in a few spots, but
it's better to have the entire tree sanitized for this rule.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 5 deletions

diff --git a/arch/sparc64/lib/rwsem.S b/arch/sparc64/lib/rwsem.S
index 174ff7b9164c..75f0e6b951d6 100644
--- a/arch/sparc64/lib/rwsem.S
+++ b/arch/sparc64/lib/rwsem.S
@@ -17,8 +17,9 @@ __down_read:
         bne,pn          %icc, 1b
          add            %g7, 1, %g7
         cmp             %g7, 0
+        membar          #StoreLoad | #StoreStore
         bl,pn           %icc, 3f
-         membar         #StoreLoad | #StoreStore
+         nop
 2:
         retl
          nop
@@ -57,8 +58,9 @@ __down_write:
         cmp             %g3, %g7
         bne,pn          %icc, 1b
          cmp            %g7, 0
+        membar          #StoreLoad | #StoreStore
         bne,pn          %icc, 3f
-         membar         #StoreLoad | #StoreStore
+         nop
 2:      retl
          nop
 3:
@@ -97,8 +99,9 @@ __up_read:
         cmp             %g1, %g7
         bne,pn          %icc, 1b
          cmp            %g7, 0
+        membar          #StoreLoad | #StoreStore
         bl,pn           %icc, 3f
-         membar         #StoreLoad | #StoreStore
+         nop
 2:      retl
          nop
 3:      sethi           %hi(RWSEM_ACTIVE_MASK), %g1
@@ -126,8 +129,9 @@ __up_write:
         bne,pn          %icc, 1b
          sub            %g7, %g1, %g7
         cmp             %g7, 0
+        membar          #StoreLoad | #StoreStore
         bl,pn           %icc, 3f
-         membar         #StoreLoad | #StoreStore
+         nop
 2:
         retl
          nop
@@ -151,8 +155,9 @@ __downgrade_write:
         bne,pn          %icc, 1b
          sub            %g7, %g1, %g7
         cmp             %g7, 0
+        membar          #StoreLoad | #StoreStore
         bl,pn           %icc, 3f
-         membar         #StoreLoad | #StoreStore
+         nop
 2:
         retl
          nop