sched, fanotify: Deal with nested sleeps

As per e23738a7300a ("sched, inotify: Deal with nested sleeps").

fanotify_read is a wait loop with sleeps in. Wait loops rely on
task_struct::state and sleeps do too, since that's the only means of
actually sleeping. Therefore the nested sleeps destroy the wait loop
state and the wait loop breaks the sleep functions that assume
TASK_RUNNING (mutex_lock).

Fix this by using the new woken_wake_function and wait_woken() stuff,
which registers wakeups in wait and thereby allows shrinking the
task_state::state changes to the actual sleep part.

Reported-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Paris <eparis@redhat.com>
Link: http://lkml.kernel.org/r/20141216152838.GZ3337@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index c991616acca9..bff8567aa42d 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -259,16 +259,15 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
         struct fsnotify_event *kevent;
         char __user *start;
         int ret;
-        DEFINE_WAIT(wait);
+        DEFINE_WAIT_FUNC(wait, woken_wake_function);
 
         start = buf;
         group = file->private_data;
 
         pr_debug("%s: group=%p\n", __func__, group);
 
+        add_wait_queue(&group->notification_waitq, &wait);
         while (1) {
-                prepare_to_wait(&group->notification_waitq, &wait, TASK_INTERRUPTIBLE);
-
                 mutex_lock(&group->notification_mutex);
                 kevent = get_one_event(group, count);
                 mutex_unlock(&group->notification_mutex);
@@ -289,7 +288,8 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
 
                         if (start != buf)
                                 break;
-                        schedule();
+
+                        wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
                         continue;
                 }
 
@@ -318,8 +318,8 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
                 buf += ret;
                 count -= ret;
         }
+        remove_wait_queue(&group->notification_waitq, &wait);
 
-        finish_wait(&group->notification_waitq, &wait);
         if (start != buf && ret != -EFAULT)
                 ret = buf - start;
         return ret;