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

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Message-Id: <20180525213331.2115471-2-arnd@arndb.de>
Date:   Fri, 25 May 2018 23:33:20 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Arnd Bergmann <arnd@...db.de>, Yonghong Song <yhs@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Song Liu <songliubraving@...com>,
        Martin KaFai Lau <kafai@...com>,
        Chenbo Feng <fengc@...gle.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH, net-next 2/2] 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@...db.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