Re: [PATCH, net-next 2/2] bpf: avoid -Wmaybe-uninitialized warning

[Song Liu]

> On May 25, 2018, at 2:33 PM, Arnd Bergmann <a...@arndb.de> wrote:
> 
> 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 <a...@arndb.de>
> ---
> kernel/bpf/stackmap.c | 7 +++----
> 1 file 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;
> -- 
> 2.9.0
> 

Acked-by: Song Liu <songliubrav...@fb.com>