Messages in this thread Patch in this message | | | Date | Thu, 14 Jul 2011 22:08:53 +0700 | From | KOBAYASHI Yoshitake <> | Subject | [PATCH RT] ipc: add a critical section in pipelined_receive |
| |
This patch is for v2.6.33.9-rt31 to avoid a deadlock. 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:446
445 while (ewp->state == STATE_PENDING) 446 cpu_relax();
Description of the problem (receiver process) 1. receiver changes sender's state to STATE_PENDING (mqueue.c:832) 2. wake up sender process and "switch to sender" (mqueue.c:833) Note: This context switch only happens in PREEMPT_RT kernel. (sender process) 3. sender check the own state in above loop (mqueue.c:445-446) *. 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> --- ipc/mqueue.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/ipc/mqueue.c b/ipc/mqueue.c index 01582e5..712d813 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -827,12 +827,17 @@ 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, -- 1.7.2.5
| |