66 lines
2.2 KiB
Diff
66 lines
2.2 KiB
Diff
Subject: ipc/mqueue: Add a critical section to avoid a deadlock
|
|
From: KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp>
|
|
Date: Sat, 23 Jul 2011 11:57:36 +0900
|
|
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/3.12/patches-3.12.6-rt9.tar.xz
|
|
|
|
(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>
|
|
---
|
|
ipc/mqueue.c | 19 ++++++++++++-------
|
|
1 file changed, 12 insertions(+), 7 deletions(-)
|
|
|
|
--- a/ipc/mqueue.c
|
|
+++ b/ipc/mqueue.c
|
|
@@ -947,13 +947,18 @@ static inline void pipelined_receive(str
|
|
wake_up_interruptible(&info->wait_q);
|
|
return;
|
|
}
|
|
- if (msg_insert(sender->msg, info))
|
|
- return;
|
|
- list_del(&sender->list);
|
|
- sender->state = STATE_PENDING;
|
|
- wake_up_process(sender->task);
|
|
- smp_wmb();
|
|
- sender->state = STATE_READY;
|
|
+ /*
|
|
+ * Keep them in one critical section for PREEMPT_RT:
|
|
+ */
|
|
+ preempt_disable_rt();
|
|
+ if (!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,
|