static void user_event_enabler_update(struct user_event *user)
{
struct user_event_enabler *enabler;
- struct user_event_mm *mm = user_event_mm_get_all(user);
struct user_event_mm *next;
+ struct user_event_mm *mm;
int attempt;
lockdep_assert_held(&event_mutex);
+ /*
+ * We need to build a one-shot list of all the mms that have an
+ * enabler for the user_event passed in. This list is only valid
+ * while holding the event_mutex. The only reason for this is due
+ * to the global mm list being RCU protected and we use methods
+ * which can wait (mmap_read_lock and pin_user_pages_remote).
+ *
+ * NOTE: user_event_mm_get_all() increments the ref count of each
+ * mm that is added to the list to prevent removal timing windows.
+ * We must always put each mm after they are used, which may wait.
+ */
+ mm = user_event_mm_get_all(user);
+
while (mm) {
next = mm->next;
mmap_read_lock(mm->mm);
struct user_event_enabler *enabler;
struct user_event_mm *mm;
+ /*
+ * We use the mm->next field to build a one-shot list from the global
+ * RCU protected list. To build this list the event_mutex must be held.
+ * This lets us build a list without requiring allocs that could fail
+ * when user based events are most wanted for diagnostics.
+ */
+ lockdep_assert_held(&event_mutex);
+
/*
* We do not want to block fork/exec while enablements are being
* updated, so we use RCU to walk the current tasks that have used