Messages in this thread Patch in this message | | | Date | Thu, 7 Mar 2013 11:26:39 +0000 | From | Eric Wong <> | Subject | epoll: possible bug from wakeup_source activation |
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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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