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Message-ID: <a8023072-0900-4be9-bb34-02850276404b@redhat.com>
Date: Mon, 8 Jan 2024 22:49:30 -0500
From: Waiman Long <longman@...hat.com>
To: Xuewen Yan <xuewen.yan@...soc.com>, peterz@...radead.org,
mingo@...hat.com, will@...nel.org, boqun.feng@...il.com
Cc: zhiguo.niu@...soc.com, ke.wang@...soc.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] lockdep: Add missing graph_unlock in check_prev_add
On 1/5/24 01:04, Xuewen Yan wrote:
> The check_prev_add() is held graph_lock, and it should unlock
> the graph_lock before return 0.
> But there is one condition where it will return 0 without unlock,
> that is:
>
> /* <prev> is not found in <next>::locks_before */
> return 0;
>
> So add graph_unlock before return 0.
>
> Fixes: 3454a36d6a39 ("lockdep: Introduce lock_list::dep")
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
> ---
> Change in V2:
> -move the graph_unlock to check_prev_add from validate_chain(Boqun)
> -Add fix tag
> ---
> ---
> kernel/locking/lockdep.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 151bd3de5936..c8602a251bec 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3178,6 +3178,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
> }
>
> /* <prev> is not found in <next>::locks_before */
> + graph_unlock();
> return 0;
> }
> }
There are multiple places in check_prev_add() that will return 0. It
will be odd to have just one of them has a graph_unlock(). It makes the
code hard to understand. You should insert graph_unlock() in a place
that matches the other places where graph_unlock() will be called. My
suggestion is as follows:
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 151bd3de5936..d9f2df36332c 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3252,7 +3252,7 @@ check_prevs_add(struct task_struct *curr, struct
held_loc>
if (hlock->check) {
int ret = check_prev_add(curr, hlock, next,
distance, &>
if (!ret)
- return 0;
+ goto out_bug;
/*
* Stop after the first non-trylock entry,
It looks like this bug was first introduced by commit 910b1b2e6d
("[PATCH] lockdep: internal locking fixes"). So you may also add a fixes
tag.
Cheers,
Longman
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