[PATCH AUTOSEL 4.20 08/60] bpf: fix lockdep false positive in stackmap

From: Sasha Levin
Date: Wed Mar 13 2019 - 15:10:43 EST


From: Alexei Starovoitov <ast@xxxxxxxxxx>

[ Upstream commit 3defaf2f15b2bfd86c6664181ac009e91985f8ac ]

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:
[ 11.214954] RIP: 0010:lock_release+0x1ad/0x280
[ 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.
Fix the warning with up_read_non_owner() and rwsem_release() annotation.

Fixes: bae77c5eb5b2 ("bpf: enable stackmap with build_id in nmi context")
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/bpf/stackmap.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index d43b14535827..950ab2f28922 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;
}

@@ -338,6 +338,12 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
} else {
work->sem = &current->mm->mmap_sem;
irq_work_queue(&work->irq_work);
+ /*
+ * The irq_work will release the mmap_sem with
+ * up_read_non_owner(). The rwsem_release() is called
+ * here to release the lock from lockdep's perspective.
+ */
+ rwsem_release(&current->mm->mmap_sem.dep_map, 1, _RET_IP_);
}
}

--
2.19.1