Subject: [PATCH bpf-next 2/4] bpf: fix lockdep false positive in stackmap

From: Alexei Starovoitov <[email-masked]>
Date: Tue, 29 Jan 2019 20:04:56 -0800

Lockdep warns about false positive:
[   11.211460] ------------[ cut here ]------------
[   11.211936] DEBUG_LOCKS_WARN_ON(depth <= 0)
[   11.211985] WARNING: CPU: 0 PID: 141 at ../kernel/locking/lockdep.c:3592 lock_release+0x1ad/0x280
[   11.213134] Modules linked in:
[   11.213413] CPU: 0 PID: 141 Comm: systemd-journal Not tainted 5.0.0-rc3-00018-g2fa53f892422-dirty #476
[   11.214191] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
[   11.214954] RIP: 0010:lock_release+0x1ad/0x280
[   11.217036] RSP: 0018:ffff88813ba03f50 EFLAGS: 00010086
[   11.217516] RAX: 000000000000001f RBX: ffff8881378d8000 RCX: 0000000000000000
[   11.218179] RDX: ffffffff810d3e9e RSI: 0000000000000001 RDI: ffffffff810d3eb3
[   11.218851] RBP: ffff8881393e2b08 R08: 0000000000000002 R09: 0000000000000000
[   11.219504] R10: 0000000000000000 R11: ffff88813ba03d9d R12: ffffffff8118dfa2
[   11.220162] R13: 0000000000000086 R14: 0000000000000000 R15: 0000000000000000
[   11.220717] FS:  00007f3c8cf35780(0000) GS:ffff88813ba00000(0000) knlGS:0000000000000000
[   11.221348] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   11.221822] CR2: 00007f5825d92080 CR3: 00000001378c8005 CR4: 00000000003606f0
[   11.222381] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   11.222951] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   11.223508] Call Trace:
[   11.223705]  <IRQ>
[   11.223874]  ? __local_bh_enable+0x7a/0x80
[   11.224199]  up_read+0x1c/0xa0
[   11.224446]  do_up_read+0x12/0x20
[   11.224713]  irq_work_run_list+0x43/0x70
[   11.225030]  irq_work_run+0x26/0x50
[   11.225310]  smp_irq_work_interrupt+0x57/0x1f0
[   11.225662]  irq_work_interrupt+0xf/0x20

since rw_semaphore is released in a different task vs task that locked the sema.
It is expected behavior.
Silence the warning by using up_read_non_owner().

Fixes: bae77c5eb5b2 ("bpf: enable stackmap with build_id in nmi context")
Acked-by: Martin KaFai Lau <[email-masked]>
Signed-off-by: Alexei Starovoitov <[email-masked]>
---
 kernel/bpf/stackmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index d43b14535827..4b79e7c251e5 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -44,7 +44,7 @@ static void do_up_read(struct irq_work *entry)
 	struct stack_map_irq_work *work;
 
 	work = container_of(entry, struct stack_map_irq_work, irq_work);
-	up_read(work->sem);
+	up_read_non_owner(work->sem);
 	work->sem = NULL;
 }
 
-- 
2.20.0