diff options
| author | KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp> | 2011-07-23 11:57:36 +0900 |
|---|---|---|
| committer | Clark Williams <williams@redhat.com> | 2012-04-13 11:01:30 -0500 |
| commit | 2913b42cc21138b374f16cab691dfbd4bb10e4e8 (patch) | |
| tree | 65e7a253a64862a9ee2b7d29565827220e52fdae | |
| parent | f7a3bbfcea5a14ce393aac43912db1979c5bc7eb (diff) | |
ipc/mqueue: Add a critical section to avoid a deadlock
(Repost for v3.0-rt1 and changed the distination addreses)
I have tested the following patch on v3.0-rt1 with PREEMPT_RT_FULL.
In POSIX message queue, if a sender process uses SCHED_FIFO and
has a higher priority than a receiver process, the sender will
be stuck at ipc/mqueue.c:452
452 while (ewp->state == STATE_PENDING)
453 cpu_relax();
Description of the problem
(receiver process)
1. receiver changes sender's state to STATE_PENDING (mqueue.c:846)
2. wake up sender process and "switch to sender" (mqueue.c:847)
Note: This context switch only happens in PREEMPT_RT_FULL kernel.
(sender process)
3. sender check the own state in above loop (mqueue.c:452-453)
*. receiver will never wake up and cannot change sender's state to
STATE_READY because sender has higher priority
Signed-off-by: Yoshitake Kobayashi <yoshitake.kobayashi@toshiba.co.jp>
Cc: viro@zeniv.linux.org.uk
Cc: dchinner@redhat.com
Cc: npiggin@kernel.dk
Cc: hch@lst.de
Cc: arnd@arndb.de
Link: http://lkml.kernel.org/r/4E2A38A0.1090601@toshiba.co.jp
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| -rw-r--r-- | ipc/mqueue.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/ipc/mqueue.c b/ipc/mqueue.c index dd9e66aa69b1..e6302726d732 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -837,15 +837,19 @@ static inline void pipelined_receive(struct mqueue_inode_info *info) wake_up_interruptible(&info->wait_q); return; } + /* + * Keep them in one critical section for PREEMPT_RT: + */ + preempt_disable_rt(); msg_insert(sender->msg, info); list_del(&sender->list); sender->state = STATE_PENDING; wake_up_process(sender->task); smp_wmb(); sender->state = STATE_READY; + preempt_enable_rt(); } - -SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr, + SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr, size_t, msg_len, unsigned int, msg_prio, const struct timespec __user *, u_abs_timeout) { |