bpf: avoid -Wmaybe-uninitialized warning

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>

1 files changed, 3 insertions, 4 deletions

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index b59ace0f0f09..b675a3f3d141 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -285,11 +285,10 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
 {
         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_offset(struct bpf_stack_build_id *id_offs,
                 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;