2020-12-30 12:04:21

by Zhang, Qiang

[permalink] [raw]
Subject: [PATCH] ipc/sem.c: Convert kfree_rcu() to call_rcu() in freeary function

From: Zqiang <[email protected]>

Due to freeary function is called with spinlock be held,
the synchronize_rcu function may be called in kfree_rcu
function, the schedule may be happen in spinlock critical
region, need to replace kfree_rcu() with call_rcu().

Fixes: 693a8b6eecce ("ipc,rcu: Convert call_rcu(free_un) to kfree_rcu()")
Signed-off-by: Zqiang <[email protected]>
---
ipc/sem.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index f6c30a85dadf..12c3184347d9 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1132,6 +1132,13 @@ static int count_semcnt(struct sem_array *sma, ushort semnum,
return semcnt;
}

+static void free_un(struct rcu_head *head)
+{
+ struct sem_undo *un = container_of(head, struct sem_undo, rcu);
+
+ kfree(un);
+}
+
/* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
* as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
* remains locked on exit.
@@ -1152,7 +1159,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
un->semid = -1;
list_del_rcu(&un->list_proc);
spin_unlock(&un->ulp->lock);
- kfree_rcu(un, rcu);
+ call_rcu(&un->rcu, free_un);
}

/* Wake up all pending processes and let them fail with EIDRM. */
--
2.17.1


2020-12-30 16:21:29

by Paul E. McKenney

[permalink] [raw]
Subject: Re: [PATCH] ipc/sem.c: Convert kfree_rcu() to call_rcu() in freeary function

On Wed, Dec 30, 2020 at 08:00:38PM +0800, [email protected] wrote:
> From: Zqiang <[email protected]>
>
> Due to freeary function is called with spinlock be held,
> the synchronize_rcu function may be called in kfree_rcu
> function, the schedule may be happen in spinlock critical
> region, need to replace kfree_rcu() with call_rcu().

Except that the call to kfree_rcu() below has two arguments, and thus
provides a link for queuing the callback. It will never directly invoke
synchronize_rcu(). It is only the single-argument variant of kfree_rcu()
that might invoke synchronize_rcu().

Or are you seeing lockdep or might-sleep failures with the current code?
If so, please post the relevant portions of the console output.

Thanx, Paul

> Fixes: 693a8b6eecce ("ipc,rcu: Convert call_rcu(free_un) to kfree_rcu()")
> Signed-off-by: Zqiang <[email protected]>
> ---
> ipc/sem.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index f6c30a85dadf..12c3184347d9 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1132,6 +1132,13 @@ static int count_semcnt(struct sem_array *sma, ushort semnum,
> return semcnt;
> }
>
> +static void free_un(struct rcu_head *head)
> +{
> + struct sem_undo *un = container_of(head, struct sem_undo, rcu);
> +
> + kfree(un);
> +}
> +
> /* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
> * as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
> * remains locked on exit.
> @@ -1152,7 +1159,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
> un->semid = -1;
> list_del_rcu(&un->list_proc);
> spin_unlock(&un->ulp->lock);
> - kfree_rcu(un, rcu);
> + call_rcu(&un->rcu, free_un);
> }
>
> /* Wake up all pending processes and let them fail with EIDRM. */
> --
> 2.17.1
>

2020-12-31 00:59:13

by Zhang, Qiang

[permalink] [raw]
Subject: 回复: [PATCH] ipc/sem.c: Convert kfree_rcu() to call_rcu() in freeary function



________________________________________
??????: Paul E. McKenney <[email protected]>
????ʱ??: 2020??12??31?? 0:19
?ռ???: Zhang, Qiang
????: [email protected]; [email protected]; [email protected]; [email protected]
????: Re: [PATCH] ipc/sem.c: Convert kfree_rcu() to call_rcu() in freeary function

On Wed, Dec 30, 2020 at 08:00:38PM +0800, [email protected] wrote:
> From: Zqiang <[email protected]>
>
> Due to freeary function is called with spinlock be held,
> the synchronize_rcu function may be called in kfree_rcu
> function, the schedule may be happen in spinlock critical
> region, need to replace kfree_rcu() with call_rcu().
>
>Except that the call to kfree_rcu() below has two arguments, and >thus
>provides a link for queuing the callback. It will never directly invoke
>synchronize_rcu(). It is only the single-argument variant of >kfree_rcu()
>that might invoke synchronize_rcu().

Sorry. It was my mistake, please ignore this patch.

Thanks
Qiang

>Or are you seeing lockdep or might-sleep failures with the current >code?
>If so, please post the relevant portions of the console output.
>
> Thanx, Paul
>
> Fixes: 693a8b6eecce ("ipc,rcu: Convert call_rcu(free_un) to kfree_rcu()")
> Signed-off-by: Zqiang <[email protected]>
> ---
> ipc/sem.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index f6c30a85dadf..12c3184347d9 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1132,6 +1132,13 @@ static int count_semcnt(struct sem_array *sma, ushort semnum,
> return semcnt;
> }
>
> +static void free_un(struct rcu_head *head)
> +{
> + struct sem_undo *un = container_of(head, struct sem_undo, rcu);
> +
> + kfree(un);
> +}
> +
> /* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
> * as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
> * remains locked on exit.
> @@ -1152,7 +1159,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
> un->semid = -1;
> list_del_rcu(&un->list_proc);
> spin_unlock(&un->ulp->lock);
> - kfree_rcu(un, rcu);
> + call_rcu(&un->rcu, free_un);
> }
>
> /* Wake up all pending processes and let them fail with EIDRM. */
> --
> 2.17.1
>