diff options
| author | KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp> | 2011-07-23 02:57:36 (GMT) |
|---|---|---|
| committer | Scott Wood <scottwood@freescale.com> | 2014-05-14 18:38:07 (GMT) |
| commit | 1ea2bfd9a1de35708a7ce5faa50156a2b1fd1227 (patch) | |
| tree | c9d93269b75c254efbc2446e57a60623e8efa6be /ipc | |
| parent | 30df975f2f4f8f021c91777b065905d001c70fed (diff) | |
| download | linux-fsl-qoriq-1ea2bfd9a1de35708a7ce5faa50156a2b1fd1227.tar.xz | |
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>
Diffstat (limited to 'ipc')
| -rw-r--r-- | ipc/mqueue.c | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/ipc/mqueue.c b/ipc/mqueue.c index af0c6bb..2276120 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -947,13 +947,18 @@ static inline void pipelined_receive(struct mqueue_inode_info *info) 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, |