fs/epoll: loosen irq safety in epoll_insert() and epoll_remove()

Both functions are similar to the context of ep_modify(), called via
epoll_ctl(2).  Just like ep_modify(), saving and restoring interrupts is
an overkill in these calls as it will never be called with irqs disabled.
While ep_remove() can be called directly from EPOLL_CTL_DEL, it can also
be called when releasing the file, but this also complies with the above.

Link: http://lkml.kernel.org/r/20180720172956.2883-3-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 2247769eb9415a4dbeecbacf3e27731e8a0bd554..1b1abc461fc03190ba3ea888bdbf27d26c9d58d0 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -762,7 +762,6 @@ static void epi_rcu_free(struct rcu_head *head)
  */
 static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 {
-       unsigned long flags;
        struct file *file = epi->ffd.file;
 
        /*
@@ -777,10 +776,10 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 
        rb_erase_cached(&epi->rbn, &ep->rbr);
 
-       spin_lock_irqsave(&ep->wq.lock, flags);
+       spin_lock_irq(&ep->wq.lock);
        if (ep_is_linked(&epi->rdllink))
                list_del_init(&epi->rdllink);
-       spin_unlock_irqrestore(&ep->wq.lock, flags);
+       spin_unlock_irq(&ep->wq.lock);
 
        wakeup_source_unregister(ep_wakeup_source(epi));
        /*
@@ -1409,7 +1408,6 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
 {
        int error, pwake = 0;
        __poll_t revents;
-       unsigned long flags;
        long user_watches;
        struct epitem *epi;
        struct ep_pqueue epq;
@@ -1476,7 +1474,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
                goto error_remove_epi;
 
        /* We have to drop the new item inside our item list to keep track of it */
-       spin_lock_irqsave(&ep->wq.lock, flags);
+       spin_lock_irq(&ep->wq.lock);
 
        /* record NAPI ID of new item if present */
        ep_set_busy_poll_napi_id(epi);
@@ -1493,7 +1491,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
                        pwake++;
        }
 
-       spin_unlock_irqrestore(&ep->wq.lock, flags);
+       spin_unlock_irq(&ep->wq.lock);
 
        atomic_long_inc(&ep->user->epoll_watches);
 
@@ -1519,10 +1517,10 @@ error_unregister:
         * list, since that is used/cleaned only inside a section bound by "mtx".
         * And ep_insert() is called with "mtx" held.
         */
-       spin_lock_irqsave(&ep->wq.lock, flags);
+       spin_lock_irq(&ep->wq.lock);
        if (ep_is_linked(&epi->rdllink))
                list_del_init(&epi->rdllink);
-       spin_unlock_irqrestore(&ep->wq.lock, flags);
+       spin_unlock_irq(&ep->wq.lock);
 
        wakeup_source_unregister(ep_wakeup_source(epi));