63 lines
2.2 KiB
Diff
63 lines
2.2 KiB
Diff
From ef6628d7653c6738f606413c6e3d65877f16a130 Mon Sep 17 00:00:00 2001
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From: KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp>
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Date: Sat, 23 Jul 2011 11:57:36 +0900
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Subject: [104/256] ipc/mqueue: Add a critical section to avoid a deadlock
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(Repost for v3.0-rt1 and changed the distination addreses)
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I have tested the following patch on v3.0-rt1 with PREEMPT_RT_FULL.
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In POSIX message queue, if a sender process uses SCHED_FIFO and
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has a higher priority than a receiver process, the sender will
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be stuck at ipc/mqueue.c:452
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452 while (ewp->state == STATE_PENDING)
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453 cpu_relax();
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Description of the problem
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(receiver process)
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1. receiver changes sender's state to STATE_PENDING (mqueue.c:846)
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2. wake up sender process and "switch to sender" (mqueue.c:847)
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Note: This context switch only happens in PREEMPT_RT_FULL kernel.
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(sender process)
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3. sender check the own state in above loop (mqueue.c:452-453)
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*. receiver will never wake up and cannot change sender's state to
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STATE_READY because sender has higher priority
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Signed-off-by: Yoshitake Kobayashi <yoshitake.kobayashi@toshiba.co.jp>
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Cc: viro@zeniv.linux.org.uk
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Cc: dchinner@redhat.com
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Cc: npiggin@kernel.dk
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Cc: hch@lst.de
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Cc: arnd@arndb.de
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Link: http://lkml.kernel.org/r/4E2A38A0.1090601@toshiba.co.jp
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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ipc/mqueue.c | 8 ++++++--
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1 file changed, 6 insertions(+), 2 deletions(-)
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diff --git a/ipc/mqueue.c b/ipc/mqueue.c
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index dd9e66a..e630272 100644
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--- a/ipc/mqueue.c
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+++ b/ipc/mqueue.c
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@@ -837,15 +837,19 @@ static inline void pipelined_receive(struct mqueue_inode_info *info)
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wake_up_interruptible(&info->wait_q);
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return;
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}
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+ /*
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+ * Keep them in one critical section for PREEMPT_RT:
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+ */
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+ preempt_disable_rt();
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msg_insert(sender->msg, info);
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list_del(&sender->list);
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sender->state = STATE_PENDING;
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wake_up_process(sender->task);
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smp_wmb();
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sender->state = STATE_READY;
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+ preempt_enable_rt();
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}
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-
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-SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr,
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+ SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr,
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size_t, msg_len, unsigned int, msg_prio,
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const struct timespec __user *, u_abs_timeout)
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{
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