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

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

[qiang.zhang]

From: Zqiang <qiang.zhang@windriver.com>

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 <qiang.zhang@windriver.com>
---
 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

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

[Paul E. McKenney]

On Wed, Dec 30, 2020 at 08:00:38PM +0800, qiang.zhang@windriver.com wrote:
> From: Zqiang <qiang.zhang@windriver.com>
> 
> 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 <qiang.zhang@windriver.com>
> ---
>  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
> 

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

[Zhang, Qiang]

________________________________________
发件人: Paul E. McKenney <paulmck@kernel.org>
发送时间: 2020年12月31日 0:19
收件人: Zhang, Qiang
抄送: akpm@linux-foundation.org; manfred@colorfullife.com; gustavoars@kernel.org; linux-kernel@vger.kernel.org
主题: Re: [PATCH] ipc/sem.c: Convert kfree_rcu() to call_rcu() in freeary function

On Wed, Dec 30, 2020 at 08:00:38PM +0800, qiang.zhang@windriver.com wrote:
> From: Zqiang <qiang.zhang@windriver.com>
>
> 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 <qiang.zhang@windriver.com>
> ---
>  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
>