On 09/03/2013 11:16 AM, Vineet Gupta wrote:
On 09/03/2013 02:27 PM, Manfred Spraul wrote:
On 09/03/2013 10:44 AM, Vineet Gupta wrote:
b) Could you check that it is not just a performance regression?
Does ./msgctl08 1000 16 hang, too?
Nope that doesn't hang. The minimal configuration that hangs reliably is msgctl
50000 2
With this config there are 3 processes.
...
555 554 root S 1208 0.4 0 0.0 ./msgctl08 50000 2
554 551 root S 1208 0.4 0 0.0 ./msgctl08 50000 2
551 496 root S 1208 0.4 0 0.0 ./msgctl08 50000 2
...
[ARCLinux]$ cat /proc/551/stack
[<80aec3c6>] do_wait+0xa02/0xc94
[<80aecad2>] SyS_wait4+0x52/0xa4
[<80ae24fc>] ret_from_system_call+0x0/0x4
[ARCLinux]$ cat /proc/555/stack
[<80c2950e>] SyS_msgrcv+0x252/0x420
[<80ae24fc>] ret_from_system_call+0x0/0x4
[ARCLinux]$ cat /proc/554/stack
[<80c28c82>] do_msgsnd+0x116/0x35c
[<80ae24fc>] ret_from_system_call+0x0/0x4
Is this a case of lost wakeup or some such. I'm running with some more diagnostics
and will report soon ...
What is the output of ipcs -q? Is the queue full or empty when it hangs?
I.e. do we forget to wake up a receiver or forget to wake up a sender?
/ # ipcs -q
------ Message Queues --------
key msqid owner perms used-bytes messages
0x72d83160 163841 root 600 0 0
Ok, a sender is sleeping - even though there are no messages in the queue.
Perhaps it is the race that I mentioned in a previous mail:
for (;;) {
struct msg_sender s;
err = -EACCES;
if (ipcperms(ns, &msq->q_perm, S_IWUGO))
goto out_unlock1;
err = security_msg_queue_msgsnd(msq, msg, msgflg);
if (err)
goto out_unlock1;
if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
1 + msq->q_qnum <= msq->q_qbytes) {
break;
}
[snip]
if (!pipelined_send(msq, msg)) {
/* no one is waiting for this message, enqueue it */
list_add_tail(&msg->m_list, &msq->q_messages);
msq->q_cbytes += msgsz;
msq->q_qnum++;
atomic_add(msgsz, &ns->msg_bytes);
The access to msq->q_cbytes is not protected.
Vineet, could you try to move the test for free space after ipc_lock?
I.e. the lock must not get dropped between testing for free space and
enqueueing the messages.
--
Manfred
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