Quoting [EMAIL PROTECTED] ([EMAIL PROTECTED]):
> PATCH [04/06]
>
> This patch introduces the .next seq operation for /proc/pid/semundo.
>
> What should be mentioned here is that the undo_list lock is released between
> between each iteration.
> Doing this, we only guarantee to access some valid data during the .show,
Ok so you count on an item sticking around for the duration of the
rcu_read_cycle(). exit_sem() is therefore not an issue. The other
possible racer is freeary() as called from IPC_RMID, but while that
could remove this entry from the undo_list->list_proc, it will wait
an rcu cycle before it actually frees it.
Am I reading that all right? If so, then:
> not to have a full coherent view of the whole list. But, oth, this reduces the
> the performance impact on the access to the undo_list.
>
> Signed-off-by: Pierre Peiffer <[EMAIL PROTECTED]>
> Signed-off-by: Nadia Derbey <[EMAIL PROTECTED]>
Acked-by: Serge Hallyn <[EMAIL PROTECTED]>
>
> ---
> ipc/sem.c | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> Index: linux-2.6.26-rc5-mm3/ipc/sem.c
> ===================================================================
> --- linux-2.6.26-rc5-mm3.orig/ipc/sem.c 2008-06-24 12:32:36.000000000
> +0200
> +++ linux-2.6.26-rc5-mm3/ipc/sem.c 2008-06-24 12:54:40.000000000 +0200
> @@ -1440,7 +1440,28 @@ static void *semundo_start(struct seq_fi
>
> static void *semundo_next(struct seq_file *m, void *v, loff_t *ppos)
> {
> - return NULL;
> + struct sem_undo *undo = v;
> + struct undo_list_data *data = m->private;
> + struct sem_undo_list *ulp = data->undo_list;
> +
> + /*
> + * No need to protect against ulp being NULL, if we are here,
> + * it can't be NULL.
> + */
> + spin_lock(&ulp->lock);
> +
> + do {
> + undo = list_entry(rcu_dereference(undo->list_proc.next),
> + struct sem_undo, list_proc);
> +
> + } while (&undo->list_proc != &ulp->list_proc && undo->semid == -1);
> +
> + ++*ppos;
> + spin_unlock(&ulp->lock);
> +
> + if (&undo->list_proc == &ulp->list_proc)
> + return NULL;
> + return undo;
> }
>
> static void semundo_stop(struct seq_file *m, void *v)
>
> --
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