netdev - Re: corrupted pvqspinlock in htab_map_update

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Date:   Mon, 1 Feb 2021 12:23:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, andrii@...nel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>, kpsingh@...nel.org,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: corrupted pvqspinlock in htab_map_update_elem

On Mon, Feb 01, 2021 at 10:50:58AM +0100, Peter Zijlstra wrote:

> >  queued_spin_unlock arch/x86/include/asm/qspinlock.h:56 [inline]
> >  lockdep_unlock+0x10e/0x290 kernel/locking/lockdep.c:124
> >  debug_locks_off_graph_unlock kernel/locking/lockdep.c:165 [inline]
> >  print_usage_bug kernel/locking/lockdep.c:3710 [inline]
> 
> Ha, I think you hit a bug in lockdep.

Something like so I suppose.

---
Subject: locking/lockdep: Avoid unmatched unlock
From: Peter Zijlstra <peterz@...radead.org>
Date: Mon Feb 1 11:55:38 CET 2021

Commit f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI"
inversions") overlooked that print_usage_bug() releases the graph_lock
and called it without the graph lock held.

Fixes: f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/locking/lockdep.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3773,7 +3773,7 @@ static void
 print_usage_bug(struct task_struct *curr, struct held_lock *this,
 		enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
 {
-	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
+	if (!debug_locks_off() || debug_locks_silent)
 		return;
 
 	pr_warn("\n");
@@ -3814,6 +3814,7 @@ valid_state(struct task_struct *curr, st
 	    enum lock_usage_bit new_bit, enum lock_usage_bit bad_bit)
 {
 	if (unlikely(hlock_class(this)->usage_mask & (1 << bad_bit))) {
+		graph_unlock()
 		print_usage_bug(curr, this, bad_bit, new_bit);
 		return 0;
 	}