alpha: fix hae_cache race in RESTORE_ALL

We want interrupts disabled on all paths leading to RESTORE_ALL;
otherwise, we are risking an IRQ coming between the updates of
alpha_mv->hae_cache and *alpha_mv->hae_register and set_hae()
within the IRQ getting badly confused.

RESTORE_ALL used to play with disabling IRQ itself, but that got
removed back in 2002, without making sure we had them disabled
on all paths.  It's cheaper to make sure we have them disabled than
to revert to original variant...

Remove the detritus left from that commit back in 2002; we used to
need a reload of $0 and $1 since swpipl would change those, but
doing that had become pointless when we stopped doing swpipl in
there...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/kernel/entry.S

@@ -73,8 +73,6 @@
 	ldq	$20, HAE_REG($19);	\
 	stq	$21, HAE_CACHE($19);	\
 	stq	$21, 0($20);		\
-	ldq	$0, 0($sp);		\
-	ldq	$1, 8($sp);		\
 99:;					\
 	ldq	$19, 72($sp);		\
 	ldq	$20, 80($sp);		\
@@ -316,7 +314,7 @@ ret_from_sys_call:
 	cmovne	$26, 0, $19		/* $19 = 0 => non-restartable */
 	ldq	$0, SP_OFF($sp)
 	and	$0, 8, $0
-	beq	$0, restore_all
+	beq	$0, ret_to_kernel
 ret_to_user:
 	/* Make sure need_resched and sigpending don't change between
 		sampling and the rti.  */
@@ -329,6 +327,11 @@ restore_all:
 	RESTORE_ALL
 	call_pal PAL_rti
 
+ret_to_kernel:
+	lda	$16, 7
+	call_pal PAL_swpipl
+	br restore_all
+
 	.align 3
 $syscall_error:
 	/*
@@ -657,7 +660,7 @@ kernel_thread:
 	/* We don't actually care for a3 success widgetry in the kernel.
 	   Not for positive errno values.  */
 	stq	$0, 0($sp)		/* $0 */
-	br	restore_all
+	br	ret_to_kernel
 .end kernel_thread
 
 /*