On Tue, Jan 29, 2019 at 08:04:56PM -0800, Alexei Starovoitov wrote:
> Lockdep warns about false positive:
This is not a false positive, and you probably also need to use
down_read_non_owner() to match this up_read_non_owner().
{up,down}_read() and {up,down}_read_non_owner() are not only different
in the lockdep annotation; there is also optimistic spin stuff that
relies on 'owner' tracking.
> [ 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 <ka...@fb.com>
> Signed-off-by: Alexei Starovoitov <a...@kernel.org>
> ---
> 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
>
