Hi Arve, looking at commit 4d7e30d98939a0340022ccd49325a3d70f7e0238
(epoll: Add a flag, EPOLLWAKEUP, to prevent suspend ...)
I think the reason for using ep->ws instead of epi->ws in the unlikely
ovflist case applies to the likely rdllist case, too. Since epi->ws is
only protected by ep->mtx, it can also be deactivated while inside
ep_poll_callback.
So something like the following patch might be necessary
(shown here with extra context):
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -968,39 +968,45 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
if (epi->next == EP_UNACTIVE_PTR) {
epi->next = ep->ovflist;
ep->ovflist = epi;
if (epi->ws) {
/*
* Activate ep->ws since epi->ws may get
* deactivated at any time.
*/
__pm_stay_awake(ep->ws);
}
}
goto out_unlock;
}
/* If this file is already in the ready list we exit soon */
if (!ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
- __pm_stay_awake(epi->ws);
+ if (epi->ws) {
+ /*
+ * Activate ep->ws since epi->ws may get
+ * deactivated at any time.
+ */
+ __pm_stay_awake(ep->ws);
+ }
}
-----------------------------------------------------------------------
However, I think my proposed patch will also cause breakage with the
way epi->ws is handled in ep_send_events_proc:
/*
* Activate ep->ws before deactivating epi->ws to prevent
* triggering auto-suspend here (in case we reactive epi->ws
* below).
*
* This could be rearranged to delay the deactivation of epi->ws
* instead, but then epi->ws would temporarily be out of sync
* with ep_is_linked().
*/
if (epi->ws && epi->ws->active)
__pm_stay_awake(ep->ws);
__pm_relax(epi->ws);
list_del_init(&epi->rdllink);
I'm not sure, but maybe only using ep->ws is the easiest way to go.
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