From: Arnd Bergmann <arnd@arndb.de>
Date: Fri, 25 May 2018 23:33:20 +0200
Subject: bpf: avoid -Wmaybe-uninitialized warning
Patch-mainline: v4.18-rc1
Git-commit: dc3b8ae9d271897e09b27fa4e4e0000de98590d1
References: bsc#1109837

The stack_map_get_build_id_offset() function is too long for gcc to track
whether 'work' may or may not be initialized at the end of it, leading
to a false-positive warning:

kernel/bpf/stackmap.c: In function 'stack_map_get_build_id_offset':
kernel/bpf/stackmap.c:334:13: error: 'work' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This removes the 'in_nmi_ctx' flag and uses the state of that variable
itself to see if it got initialized.

Fixes: bae77c5eb5b2 ("bpf: enable stackmap with build_id in nmi context")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/stackmap.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -285,11 +285,10 @@ static void stack_map_get_build_id_offse
 {
 	int i;
 	struct vm_area_struct *vma;
-	bool in_nmi_ctx = in_nmi();
 	bool irq_work_busy = false;
-	struct stack_map_irq_work *work;
+	struct stack_map_irq_work *work = NULL;
 
-	if (in_nmi_ctx) {
+	if (in_nmi()) {
 		work = this_cpu_ptr(&up_read_work);
 		if (work->irq_work.flags & IRQ_WORK_BUSY)
 			/* cannot queue more up_read, fallback */
@@ -328,7 +327,7 @@ static void stack_map_get_build_id_offse
 		id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
 	}
 
-	if (!in_nmi_ctx) {
+	if (!work) {
 		up_read(&current->mm->mmap_sem);
 	} else {
 		work->sem = &current->mm->mmap_sem;