[BUG] A thread is stuck waiting to close an SRT socket due to an internal SRT mutex lock. #2944
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tvaknin
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tvaknin
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From the provided stack traces it is not clear who holds the But from the state of the GC thread that above described case is not the one happening here. |
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Could this problem be reproduced with having #2893 added? |
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Thread sanitizer shows a potential deadlock around those functions:
Full Threat ReportClick to expand |
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There was some PR where m_ConnectionLock was taken out for the call to closeInternal(), but I don't remember the details. The inversion between m_LSLock and m_ConnectionLock is known, but it was later proven that these two things can never happen simultaneously - it's just detected by the thread sanitizer that these two cases may happen in theory. It would be nice to dissolve them, but no sensible way to fix it was found. |
I can try this next week |
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I tried the fix using the branch "dev-add-socket-busy-counter". I can reproduce the same problem. let me know if you need more info. |
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We need somehow to identify who is holding the mutex (see my comment above). Can you check other threads? There should be some trying to lock another mutex while |
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You may try the fix in #2032. I can't find any PR with that fix which does unlocking for the time of closeInternal(). |
Attached full BT of all threads. |
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I see 7 threads calling This issue is likely similar to #2252. |
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Just took a quick look - |
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And the only other thing I can see where any of the SRT threads is standing is |
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if (!self->m_bClosing)
{
self->m_pSndUList->waitNonEmpty();
IF_DEBUG_HIGHRATE(self->m_WorkerStats.lCondWait++);
}while this notification is also being missed srt::CSndQueue::~CSndQueue()
{
m_bClosing = true;
if (m_pTimer != NULL)
{
m_pTimer->interrupt();
}
// Unblock CSndQueue worker thread if it is waiting.
m_pSndUList->signalInterrupt(); |
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Hi everyone,
Potential issue: A thread is stuck waiting to close an SRT socket due to an internal SRT mutex lock.
The Backtrace of the thread being blocked:
#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:103 #1 0x00007f6ad3751411 in __GI___pthread_mutex_lock (mutex=0x7f6ad4c1e480 <srt::CUDT::uglobal()::instance+96>) at ../nptl/pthread_mutex_lock.c:80 #2 0x00007f6ad4b53b33 in srt::CUDTUnited::locateSocket(int, srt::CUDTUnited::ErrorHandling) () from ../libs/libsrt.so.1.5 #3 0x00007f6ad4b5bc58 in srt::CUDTUnited::close(int) () from ../libs/libsrt.so.1.5 #4 0x00007f6ad4b5bcec in srt::CUDT::close(int) () from ../libs/libsrt.so.1.5 #5 0x00000000004c1e78 in SrtConnectionManager::CheckForConnection (this=0x10ecea0 <SrtConnectionManager::GetInstance()::inst>) at muxer/SrtConnectionManager.cpp:244I have a few more threads ~6 that are also stuck on this Mutex. e.g.
#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:103 #1 0x00007f954a5e0411 in __GI___pthread_mutex_lock (mutex=0x7f954baad480 <srt::CUDT::uglobal()::instance+96>) at ../nptl/pthread_mutex_lock.c:80 #2 0x00007f954b9e2b33 in srt::CUDTUnited::locateSocket(int, srt::CUDTUnited::ErrorHandling) () from../libs/libsrt.so.1.5 #3 0x00007f954b9e623c in srt::CUDT::sendmsg2(int, char const*, int, SRT_MsgCtrl_&) () from ../libs/libsrt.so.1.5 #4 0x00007f954b9e629f in srt::CUDT::send(int, char const*, int, int) () from ../libs/libsrt.so.1.5 #5 0x00000000004dad3d in OutSrtSocket::Send (successCnt=0x2f8d484, this=0x7f950194eeb0) at Revioly/OutSrtSocket.cpp:32I also found that the SRT thread "SRT:GC" holds it too:
41 Thread 0x7f94feffd700 (LWP 32188) "SRT:GC" __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:103
#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:103 #1 0x00007f954a5e0411 in __GI___pthread_mutex_lock (mutex=0x7f954baad480 <srt::CUDT::uglobal()::instance+96>) at ../nptl/pthread_mutex_lock.c:80 #2 0x00007f954b9ed00e in srt::CUDTUnited::checkBrokenSockets() () from ../libs/libsrt.so.1.5 #3 0x00007f954b9ed6a8 in srt::CUDTUnited::garbageCollect(void*) () from ../libs/libsrt.so.1.5 #4 0x00007f954a5ddefc in start_thread (arg=<optimized out>) at pthread_create.c:479 #5 0x00007f9549ec122f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95SRT internal sockets thread example:
#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:103 #1 0x00007f954a5e0411 in __GI___pthread_mutex_lock (mutex=0x7f954baad480 <srt::CUDT::uglobal()::instance+96>) at ../nptl/pthread_mutex_lock.c:80 #2 0x00007f954b9ebfb8 in srt::CUDTUnited::newConnection(int, srt::sockaddr_any const&, srt::CPacket const&, srt::CHandShake&, int&, srt::CUDT*&) () from ../libs/libsrt.so.1.5 #3 0x00007f954ba1948d in srt::CUDT::processConnectRequest(srt::sockaddr_any const&, srt::CPacket&) () from ../libs/libsrt.so.1.5 #4 0x00007f954ba60156 in srt::CRcvQueue::worker_ProcessConnectionRequest(srt::CUnit*, srt::sockaddr_any const&) () from ../libs/libsrt.so.1.5 #5 0x00007f954ba60ec4 in srt::CRcvQueue::worker(void*) () from ../libs/libsrt.so.1.5 #6 0x00007f954a5ddefc in start_thread (arg=<optimized out>) at pthread_create.c:479 #7 0x00007f9549ec122f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95To Reproduce
Steps to reproduce the behavior:
No problem in SRT versions 1.5.1 or 1.5.2 (I didn't check 1.5.2) But, I found the issue in version 1.5.3.
My setup has 70 SRT sockets (Senders - listeners), setting the SRT latency to 6000ms.
The trouble starts in the Sender-Listener device right after the downstream device (Receiver-Caller) restarts or loses connection.
Desktop
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