runtime: ignore failure from madvise

When we release memory to the OS, if the OS doesn't want us
to release it (for example, because the program executed
mlockall(MCL_FUTURE)), madvise will fail. Ignore the failure
instead of crashing.

Fixes #3435.

R=ken2
CC=golang-dev
https://golang.org/cl/6998052

src/pkg/runtime/sys_darwin_386.s

@@ -47,8 +47,7 @@ TEXT runtime·mmap(SB),7,$0
 TEXT runtime·madvise(SB),7,$0
 	MOVL	$75, AX
 	INT	$0x80
-	JAE	2(PC)
-	MOVL	$0xf1, 0xf1  // crash
+	// ignore failure - maybe pages are locked
 	RET
 
 TEXT runtime·munmap(SB),7,$0

src/pkg/runtime/sys_darwin_amd64.s

@@ -61,8 +61,7 @@ TEXT runtime·madvise(SB), 7, $0
 	MOVL	24(SP), DX		// arg 3 advice
 	MOVL	$(0x2000000+75), AX	// syscall entry madvise
 	SYSCALL
-	JCC	2(PC)
-	MOVL	$0xf1, 0xf1  // crash
+	// ignore failure - maybe pages are locked
 	RET
 
 // OS X comm page time offsets

src/pkg/runtime/sys_freebsd_386.s

@@ -105,8 +105,7 @@ TEXT runtime·munmap(SB),7,$-4
 TEXT runtime·madvise(SB),7,$-4
 	MOVL	$75, AX	// madvise
 	INT	$0x80
-	JAE	2(PC)
-	MOVL	$0xf1, 0xf1  // crash
+	// ignore failure - maybe pages are locked
 	RET
 
 TEXT runtime·setitimer(SB), 7, $-4

src/pkg/runtime/sys_freebsd_amd64.s

@@ -188,8 +188,7 @@ TEXT runtime·madvise(SB),7,$0
 	MOVQ	24(SP), DX
 	MOVQ	$75, AX	// madvise
 	SYSCALL
-	JCC	2(PC)
-	MOVL	$0xf1, 0xf1  // crash
+	// ignore failure - maybe pages are locked
 	RET
 	
 TEXT runtime·sigaltstack(SB),7,$-8

src/pkg/runtime/sys_freebsd_arm.s

@@ -189,8 +189,7 @@ TEXT runtime·madvise(SB),7,$0
 	MOVW 4(FP), R1		// arg 2 len
 	MOVW 8(FP), R2		// arg 3 flags
 	SWI $75
-	MOVW.CS $0, R9 // crash on syscall failure
-	MOVW.CS R9, (R9)
+	// ignore failure - maybe pages are locked
 	RET
 	
 TEXT runtime·sigaltstack(SB),7,$-8

src/pkg/runtime/sys_linux_386.s

@@ -241,9 +241,7 @@ TEXT runtime·madvise(SB),7,$0
 	MOVL	8(SP), CX
 	MOVL	12(SP), DX
 	CALL	*runtime·_vdso(SB)
-	CMPL	AX, $0xfffff001
-	JLS	2(PC)
-	INT $3
+	// ignore failure - maybe pages are locked
 	RET
 
 // int32 futex(int32 *uaddr, int32 op, int32 val,

src/pkg/runtime/sys_linux_amd64.s

@@ -250,9 +250,7 @@ TEXT runtime·madvise(SB),7,$0
 	MOVQ	24(SP), DX
 	MOVQ	$28, AX	// madvise
 	SYSCALL
-	CMPQ	AX, $0xfffffffffffff001
-	JLS	2(PC)
-	MOVL	$0xf1, 0xf1  // crash
+	// ignore failure - maybe pages are locked
 	RET
 
 // int64 futex(int32 *uaddr, int32 op, int32 val,

src/pkg/runtime/sys_linux_arm.s

@@ -133,10 +133,7 @@ TEXT runtime·madvise(SB),7,$0
 	MOVW	8(FP), R2
 	MOVW	$SYS_madvise, R7
 	SWI	$0
-	MOVW	$0xfffff001, R6
-	CMP 	R6, R0
-	MOVW.HI	$0, R9  // crash on syscall failure
-	MOVW.HI	R9, (R9)
+	// ignore failure - maybe pages are locked
 	RET
 
 TEXT runtime·setitimer(SB),7,$0

src/pkg/runtime/sys_netbsd_386.s

@@ -86,8 +86,7 @@ TEXT runtime·munmap(SB),7,$-4
 TEXT runtime·madvise(SB),7,$-4
 	MOVL	$75, AX			// sys_madvise
 	INT	$0x80
-	JAE	2(PC)
-	MOVL	$0xf1, 0xf1		// crash
+	// ignore failure - maybe pages are locked
 	RET
 
 TEXT runtime·setitimer(SB),7,$-4

src/pkg/runtime/sys_netbsd_amd64.s

@@ -252,8 +252,7 @@ TEXT runtime·madvise(SB),7,$0
 	MOVQ	behav+16(FP), DX	// arg 3 - behav
 	MOVQ	$75, AX			// sys_madvise
 	SYSCALL
-	JCC	2(PC)
-	MOVL	$0xf1, 0xf1		// crash
+	// ignore failure - maybe pages are locked
 	RET
 
 TEXT runtime·sigaltstack(SB),7,$-8

src/pkg/runtime/sys_openbsd_amd64.s

@@ -240,8 +240,7 @@ TEXT runtime·madvise(SB),7,$0
 	MOVQ	behav+16(FP), DX	// arg 3 - behav
 	MOVQ	$75, AX			// sys_madvise
 	SYSCALL
-	JCC	2(PC)
-	MOVL	$0xf1, 0xf1		// crash
+	// ignore failure - maybe pages are locked
 	RET
 
 TEXT runtime·sigaltstack(SB),7,$-8