[PATCH 0/4] audit: refactor and fix for potential deadlock

[Eiichi Tsukata]

Commit 7ffb8e317bae ("audit: we don't need to
__set_current_state(TASK_RUNNING)") accidentally moved queue full check
before add_wait_queue_exclusive() which introduced the following race:

    CPU1                           CPU2
  ========                       ========
  (in audit_log_start())         (in kauditd_thread())

  queue is full
                                 wake_up(&audit_backlog_wait)
                                 wait_event_freezable()
  add_wait_queue_exclusive()
  ...
  schedule_timeout()

Once this happens, both audit_log_start() and kauditd_thread() can cause
deadlock for up to backlog_wait_time waiting for each other. To prevent
the race, this patch adds queue full check after
prepare_to_wait_exclusive().

This patchset consists of the following parts:

Patch 1-3: Refactorings and a small fix preferable for deadlock fix
Patch 4: Actual deadlock fix

Eiichi Tsukata (4):
  audit: refactor queue full checks
  audit: account backlog waiting time in audit_receive()
  audit: convert DECLARE_WAITQUEUE to DEFINE_WAIT
  audit: check if queue is full after prepare_to_wait_exclusive()

 kernel/audit.c | 71 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 43 insertions(+), 28 deletions(-)

-- 
2.40.0