Quoting Nadia.Derbey@xxxxxxxx (Nadia.Derbey@xxxxxxxx):
> PATCH [03/06]
>
> This patch introduces the .start and .stop seq operations for
> /proc/pid/semundo.
>
> Signed-off-by: Pierre Peiffer <pierre.peiffer@xxxxxxxx>
> Signed-off-by: Nadia Derbey <Nadia.Derbey@xxxxxxxx>
Acked-by: Serge Hallyn <serue@xxxxxxxxxx>
> ---
> ipc/sem.c | 43 +++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 41 insertions(+), 2 deletions(-)
>
> Index: linux-2.6.26-rc5-mm3/ipc/sem.c
> ===================================================================
> --- linux-2.6.26-rc5-mm3.orig/ipc/sem.c 2008-06-24 10:59:46.000000000 +0200
> +++ linux-2.6.26-rc5-mm3/ipc/sem.c 2008-06-24 12:32:36.000000000 +0200
> @@ -1400,7 +1400,42 @@ struct undo_list_data {
> /* iterator */
> static void *semundo_start(struct seq_file *m, loff_t *ppos)
> {
> - return NULL;
> + struct undo_list_data *data = m->private;
> + struct sem_undo_list *ulp = data->undo_list;
> + struct sem_undo *undo;
> + loff_t pos = *ppos;
> +
> + if (!ulp)
> + return NULL;
> +
> + if (pos < 0)
> + return NULL;
> +
> + /* If ulp is not NULL, it means that we've successfully grabbed
> + * a refcnt in semundo_open. That prevents the undo_list from being
> + * freed.
> + *
> + * Note:
> + * 1) the sem_undo structure is RCU-protected. So take the rcu read
> + * lock and only release it during the .stop operation.
> + * 2) we accept to release the undo_list lock (i.e. we allow the list
> + * to change) between each iteration, instead of taking that lock
> + * during the .start and releasing it during the .stop operation.
> + * This is to reduce the performance impact on the access to the
> + * undo_list.
> + */
> + rcu_read_lock();
> + spin_lock(&ulp->lock);
> + list_for_each_entry_rcu(undo, &ulp->list_proc, list_proc) {
> + if ((undo->semid != -1) && !(pos--))
> + break;
> + }
> + spin_unlock(&ulp->lock);
> +
> + if (&undo->list_proc == &ulp->list_proc)
> + return NULL;
> +
> + return undo;
> }
>
> static void *semundo_next(struct seq_file *m, void *v, loff_t *ppos)
> @@ -1410,7 +1445,11 @@ static void *semundo_next(struct seq_fil
>
> static void semundo_stop(struct seq_file *m, void *v)
> {
> - return;
> + struct undo_list_data *data = m->private;
> + struct sem_undo_list *ulp = data->undo_list;
> +
> + if (ulp)
> + rcu_read_unlock();
> }
>
> static int semundo_show(struct seq_file *m, void *v)
>
> --
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