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From: Peter Zijlstra <peterz@infradead.org>
To: Boqun Feng <boqun.feng@gmail.com>, g@hirez.programming.kicks-ass.net
Cc: Qian Cai <cai@redhat.com>, Waiman Long <longman@redhat.com>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: lockdep null-ptr-deref
Date: Wed, 30 Sep 2020 11:16:10 +0200	[thread overview]
Message-ID: <20200930091610.GV2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200929230823.GC17810@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net>

On Wed, Sep 30, 2020 at 07:08:23AM +0800, Boqun Feng wrote:
> I think there are two problems here:
> 
> 1) the "(null)" means we don't have the "usage_str" for a usage bit,
> which I think is the LOCK_USED_READ bit introduced by Peter at
> 23870f122768 ('locking/lockdep: Fix "USED" <- "IN-NMI" inversions').
> 
> 2) the next null-ptr-deref, and I think this is also caused by
> LOCK_USED_READ bit, because in the loop inside
> print_lock_class_header(), we iterate from 0 to LOCK_USAGE_STATES (which
> is 4*2 + 3), however the class->usage_traces[] only has
> XXX_LOCK_USAGE_STATES (which is 4*2 + 1) elements, so if we have
> LOCK_USED_READ bit set in ->usage_mask, we will try to access an element
> out of the ->usage_traces[] array.
> 
> Probably the following helps? And another possible fix is to enlarge the
> ->usage_trace[] array and record the call trace of LOCK_READ_USED.

Urgh.. yeah, I wanted to avoid saving that trace; it's pretty useless :/
The existing USED trace is already mostly pointless, the consistent
thing would be to remove both but that might be too radical.

But you're right in that I made a right mess of it. Not sure what's
best here.

Let me have a play.

  reply	other threads:[~2020-09-30  9:16 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-29 14:31 lockdep null-ptr-deref Qian Cai
2020-09-29 23:08 ` Boqun Feng
2020-09-30  9:16   ` Peter Zijlstra [this message]
2020-09-30  9:49     ` Peter Zijlstra
2020-09-30 12:18       ` Boqun Feng
2020-09-30 19:02         ` Peter Zijlstra
2020-10-02 12:36           ` Boqun Feng
2020-10-02 13:09             ` Peter Zijlstra
2020-10-02 13:35               ` Boqun Feng
2020-10-02 10:06       ` Peter Zijlstra
2020-10-02 13:40         ` Qian Cai
2020-10-07 16:20       ` [tip: locking/core] lockdep: Fix usage_traceoverflow tip-bot2 for Peter Zijlstra
2020-10-27 11:29         ` Chris Wilson
2020-10-27 11:59           ` Peter Zijlstra
2020-10-27 12:30             ` Peter Zijlstra
2020-10-27 12:48               ` Peter Zijlstra
2020-10-27 14:13                 ` Chris Wilson
2020-10-31 11:30                 ` [tip: locking/urgent] lockdep: Fix nr_unused_locks accounting tip-bot2 for Peter Zijlstra
2020-10-27 13:29               ` [tip: locking/core] lockdep: Fix usage_traceoverflow Chris Wilson
2020-10-27 15:45                 ` Peter Zijlstra
2020-10-27 16:34                   ` Chris Wilson
2020-10-28 17:40                     ` Chris Wilson
2020-10-28 18:06                       ` Chris Wilson
2020-10-28 19:42                       ` Peter Zijlstra
2020-10-28 19:59                         ` Peter Zijlstra
2020-10-30  3:51                           ` Boqun Feng
2020-10-30  9:38                             ` Peter Zijlstra
2020-10-30  9:55                               ` Peter Zijlstra
2020-11-02  5:37                               ` [PATCH 1/2] lockdep: Avoid to modify chain keys in validate_chain() Boqun Feng
2020-11-02  5:37                                 ` [PATCH 2/2] lockdep/selftest: Add spin_nest_lock test Boqun Feng
2020-12-03 10:35                                   ` [tip: locking/core] " tip-bot2 for Boqun Feng
2020-11-05  6:25                                 ` [PATCH 1/2] lockdep: Avoid to modify chain keys in validate_chain() Boqun Feng
2020-11-10 17:28                                 ` Peter Zijlstra
2020-11-11  8:23                                 ` [tip: locking/urgent] " tip-bot2 for Boqun Feng
2020-10-09  7:58       ` [tip: locking/core] lockdep: Fix usage_traceoverflow tip-bot2 for Peter Zijlstra

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