sparc64: Rearrange thread info to cheaply clear syscall noerror state.

After fixing a couple of brainos, it even seems to work.  What's done here
is move of ->syscall_noerror right before FPDEPTH byte in ->flags and
using sth to [%g6 + TI_SYS_NOERROR] instead of stb to [%g6 + TI_FPDEPTH] in
both branches of etrap_save.  AFAICS, that ought to be solid.  Again,
deciding what to do with now unused delay slot of branch on ->syscall_noerror
and dealing with the order of tests in ret_from_sys is a separate question,
but at least that way we don't have to clean ->syscall_noerror in there at
all.  AFAICS, it ought to be a clear win - sth is not going to cost more than
stb on etrap_64.S side of things, and we are losing write on syscalls.S one.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 8 insertions, 6 deletions

diff --git a/arch/sparc/kernel/etrap_64.S b/arch/sparc/kernel/etrap_64.S
index 786b185e6e3f..1276ca2567ba 100644
--- a/arch/sparc/kernel/etrap_64.S
+++ b/arch/sparc/kernel/etrap_64.S
@@ -92,8 +92,10 @@ etrap_save:	save	%g2, -STACK_BIAS, %sp
                 rdpr    %wstate, %g2
                 wrpr    %g0, 0, %canrestore
                 sll     %g2, 3, %g2
+
+                /* Set TI_SYS_FPDEPTH to 1 and clear TI_SYS_NOERROR.  */
                 mov     1, %l5
-                stb     %l5, [%l6 + TI_FPDEPTH]
+                sth     %l5, [%l6 + TI_SYS_NOERROR]
 
                 wrpr    %g3, 0, %otherwin
                 wrpr    %g2, 0, %wstate
@@ -152,7 +154,9 @@ etrap_save:	save	%g2, -STACK_BIAS, %sp
                 add     %l6, TI_FPSAVED + 1, %l4
                 srl     %l5, 1, %l3
                 add     %l5, 2, %l5
-                stb     %l5, [%l6 + TI_FPDEPTH]
+
+                /* Set TI_SYS_FPDEPTH to %l5 and clear TI_SYS_NOERROR.  */
+                sth     %l5, [%l6 + TI_SYS_NOERROR]
                 ba,pt   %xcc, 2b
                  stb    %g0, [%l4 + %l3]
                 nop
diff --git a/arch/sparc/kernel/syscalls.S b/arch/sparc/kernel/syscalls.S
index 1d7e274f3f2b..ed277e2fdfc8 100644
--- a/arch/sparc/kernel/syscalls.S
+++ b/arch/sparc/kernel/syscalls.S
@@ -221,8 +221,8 @@ ret_sys_call:
          * was invoked.
          */
         ldub    [%g6 + TI_SYS_NOERROR], %l2
-        brnz,a,pn %l2, 80f
-         stb    %g0, [%g6 + TI_SYS_NOERROR]
+        brnz,pn %l2, 80f
+         nop
 
         cmp     %o0, -ERESTART_RESTARTBLOCK
         bgeu,pn %xcc, 1f
diff --git a/arch/sparc/kernel/traps_64.c b/arch/sparc/kernel/traps_64.c
index fa1f1d375ffc..82af591fe43f 100644
--- a/arch/sparc/kernel/traps_64.c
+++ b/arch/sparc/kernel/traps_64.c
@@ -2547,8 +2547,6 @@ void __init trap_init(void)
                      TI_PRE_COUNT != offsetof(struct thread_info,
                                               preempt_count) ||
                      TI_NEW_CHILD != offsetof(struct thread_info, new_child) ||
-                     TI_SYS_NOERROR != offsetof(struct thread_info,
-                                                syscall_noerror) ||
                      TI_RESTART_BLOCK != offsetof(struct thread_info,
                                                   restart_block) ||
                      TI_KUNA_REGS != offsetof(struct thread_info,