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 <[email protected]>
Signed-off-by: Zhiguo Niu <[email protected]>
---
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;
}
}
--
2.25.1
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 <[email protected]>
> Signed-off-by: Zhiguo Niu <[email protected]>
> ---
> 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
Hi Waiman
On Tue, Jan 9, 2024 at 11:51 AM Waiman Long <[email protected]> wrote:
>
> 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 <[email protected]>
> > Signed-off-by: Zhiguo Niu <[email protected]>
> > ---
> > 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,
>
As you say, there are multiple places in check_prev_add() that will
return 0, and some cases had unlocked the lock, if all goto the
out_bug, would it cause double unlock?
Maybe as follows?
---
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 151bd3de5936..8b665ba90ad0 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3178,7 +3178,7 @@ check_prev_add(struct task_struct *curr, struct
held_lock *prev,
}
/* <prev> is not found in <next>::locks_before */
- return 0;
+ goto list_err;
}
}
@@ -3215,6 +3215,11 @@ check_prev_add(struct task_struct *curr, struct
held_lock *prev,
return 0;
return 2;
+
+list_err:
+ /* still get graph_lock, unlock it before return*/
+ graph_unlock();
+ return 0;
}
Thanks!
---
BRs
xuewen
> 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
>
>
On 1/9/24 00:11, Xuewen Yan wrote:
> Hi Waiman
>
>
> On Tue, Jan 9, 2024 at 11:51 AM Waiman Long <[email protected]> wrote:
>> 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 <[email protected]>
>>> Signed-off-by: Zhiguo Niu <[email protected]>
>>> ---
>>> 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,
>>
> As you say, there are multiple places in check_prev_add() that will
> return 0, and some cases had unlocked the lock, if all goto the
> out_bug, would it cause double unlock?
> Maybe as follows?
> ---
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 151bd3de5936..8b665ba90ad0 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3178,7 +3178,7 @@ check_prev_add(struct task_struct *curr, struct
> held_lock *prev,
> }
>
> /* <prev> is not found in <next>::locks_before */
> - return 0;
> + goto list_err;
> }
> }
>
> @@ -3215,6 +3215,11 @@ check_prev_add(struct task_struct *curr, struct
> held_lock *prev,
> return 0;
>
> return 2;
> +
> +list_err:
> + /* still get graph_lock, unlock it before return*/
> + graph_unlock();
> + return 0;
> }
I see. the graph_unlock() is called before any error message is printed.
I understand the reason why this is done this way, but it does make it
easy to re-introduce this kind of error when the lockdep code is
changed. We need a better system to track the state of the graph_lock
and do an unlock if necessary.
Cheers,
Longman