[MIPS] Fix potential latency problem due to non-atomic cpu_wait.

If an interrupt happened between checking of NEED_RESCHED and WAIT
instruction, adjust EPC to restart from checking of NEED_RESCHED.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 16 insertions, 6 deletions

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 6bee29097a56..5fd0cd020af5 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -46,6 +46,9 @@
 #include <asm/types.h>
 #include <asm/stacktrace.h>
 
+extern void check_wait(void);
+extern asmlinkage void r4k_wait(void);
+extern asmlinkage void rollback_handle_int(void);
 extern asmlinkage void handle_int(void);
 extern asmlinkage void handle_tlbm(void);
 extern asmlinkage void handle_tlbl(void);
@@ -1251,6 +1254,9 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
 
                 extern char except_vec_vi, except_vec_vi_lui;
                 extern char except_vec_vi_ori, except_vec_vi_end;
+                extern char rollback_except_vec_vi;
+                char *vec_start = (cpu_wait == r4k_wait) ?
+                        &rollback_except_vec_vi : &except_vec_vi;
 #ifdef CONFIG_MIPS_MT_SMTC
                 /*
                  * We need to provide the SMTC vectored interrupt handler
@@ -1258,11 +1264,11 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
                  * Status.IM bit to be masked before going there.
                  */
                 extern char except_vec_vi_mori;
-                const int mori_offset = &except_vec_vi_mori - &except_vec_vi;
+                const int mori_offset = &except_vec_vi_mori - vec_start;
 #endif /* CONFIG_MIPS_MT_SMTC */
-                const int handler_len = &except_vec_vi_end - &except_vec_vi;
-                const int lui_offset = &except_vec_vi_lui - &except_vec_vi;
-                const int ori_offset = &except_vec_vi_ori - &except_vec_vi;
+                const int handler_len = &except_vec_vi_end - vec_start;
+                const int lui_offset = &except_vec_vi_lui - vec_start;
+                const int ori_offset = &except_vec_vi_ori - vec_start;
 
                 if (handler_len > VECTORSPACING) {
                         /*
@@ -1272,7 +1278,7 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
                         panic("VECTORSPACING too small");
                 }
 
-                memcpy(b, &except_vec_vi, handler_len);
+                memcpy(b, vec_start, handler_len);
 #ifdef CONFIG_MIPS_MT_SMTC
                 BUG_ON(n > 7);  /* Vector index %d exceeds SMTC maximum. */
 
@@ -1554,6 +1560,10 @@ void __init trap_init(void)
         extern char except_vec3_generic, except_vec3_r4000;
         extern char except_vec4;
         unsigned long i;
+        int rollback;
+
+        check_wait();
+        rollback = (cpu_wait == r4k_wait);
 
 #if defined(CONFIG_KGDB)
         if (kgdb_early_setup)
@@ -1618,7 +1628,7 @@ void __init trap_init(void)
         if (board_be_init)
                 board_be_init();
 
-        set_except_vector(0, handle_int);
+        set_except_vector(0, rollback ? rollback_handle_int : handle_int);
         set_except_vector(1, handle_tlbm);
         set_except_vector(2, handle_tlbl);
         set_except_vector(3, handle_tlbs);