[PATCH] powerpc: Ensure gcc doesn't move around cache flushing in __patch_instruction

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

The current asm statement in __patch_instruction() for the cache flushes
doesn't have a "volatile" statement and no memory clobber. That means
gcc can potentially move it around (or move the store done by put_user
past the flush).

Add both to ensure gcc doesn't play games.

Found by code inspection, no actual bug reported.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -32,8 +32,9 @@ static int __patch_instruction(unsigned int *exec_addr, unsigned int instr,
        if (err)
                return err;
 
-       asm ("dcbst 0, %0; sync; icbi 0,%1; sync; isync" :: "r" (patch_addr),
-                                                           "r" (exec_addr));
+       asm volatile("dcbst 0, %0; sync; icbi 0,%1; sync; isync"
+                    :: "r" (patch_addr), "r" (exec_addr)
+                    : "memory");
 
        return 0;
 }