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

[Zhang, Qiang]

________________________________________
发件人: Paul E. McKenney <paulmck@xxxxxxxxxx>
发送时间: 2020年12月31日 0:19
收件人: Zhang, Qiang
抄送: akpm@xxxxxxxxxxxxxxxxxxxx; manfred@xxxxxxxxxxxxxxxx; gustavoars@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
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@xxxxxxxxxxxxx wrote:
> From: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> ---
>  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
>