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From "ASF subversion and git services (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (QPID-6157) linearstore: segfault when 2 journals request new journal file from empty EFP
Date Fri, 17 Oct 2014 08:22:34 GMT

    [ https://issues.apache.org/jira/browse/QPID-6157?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14174844#comment-14174844
] 

ASF subversion and git services commented on QPID-6157:
-------------------------------------------------------

Commit 1632504 from [~pmoravec] in branch 'qpid/trunk'
[ https://svn.apache.org/r1632504 ]

QPID-6157: linearstore: segfault when 2 journals request new journal file from empty EFP

> linearstore: segfault when 2 journals request new journal file from empty EFP
> -----------------------------------------------------------------------------
>
>                 Key: QPID-6157
>                 URL: https://issues.apache.org/jira/browse/QPID-6157
>             Project: Qpid
>          Issue Type: Bug
>          Components: C++ Broker
>    Affects Versions: 0.30
>            Reporter: Pavel Moravec
>            Assignee: Pavel Moravec
>              Labels: patch
>
> Description of problem:
> Broker using linearstore module can segfault when:
> - EFP is empty
> - 2 journals concurrently request new journal file from EFP
> There is a race condition described in Additional info that leads to segfault.
> Version-Release number of selected component (if applicable):
> any
> How reproducible:
> 100% in few minutes (on faster machines)
> Steps to Reproduce:
> Reproducer script:
> topics=10
> queues_per_topic=10
> rm -rf /var/lib/qpidd/* /tmp/qpidd.log
> service qpidd restart
> echo "$(date): creating $(($((topics))*$((queues_per_topic)))) queues"
> for i in $(seq 1 $topics); do
>   for j in $(seq 1 $queues_per_topic); do
>     qpid-receive -a "Durable_${i}_${j}; {create:always, node:{durable:true, x-bindings:[{exchange:'amq.direct',
queue:'Durable_${i}_${j}', key:'${i}'}] }}" &
>   done
> done
> wait
> echo "$(date): queues created"
> while true; do
>   echo "$(date): publishing messages.."
>   for i in $(seq 1 $topics); do
>     qpid-send -a "amq.direct/${i}" -m 1000000 --durable=yes --content-size=1000 &
>   done
>   wait
>   echo "$(date): consuming messages.."
>   for i in $(seq 1 $topics); do
>     for j in $(seq 1 $queues_per_topic); do
>       qpid-receive -a "Durable_${i}_${j}" -m 1000000 --print-content=no &
>     done
>   done
>   wait
> done
> #end of the script
> Actual results:
> segfault with bt:
> Thread 1 (Thread 0x7ff85b3f1700 (LWP 17810)):
> #0  0x00007ff9927104f3 in std::basic_string<char, std::char_traits<char>, std::allocator<char>
>::assign(std::basic_string<char, std::char_traits<char>, std::allocator<char>
> const&) () from /usr/lib64/libstdc++.so.6
> No symbol table info available.
> #1  0x00007ff98e59d6a1 in operator= (this=0x1ab3480) at /usr/include/c++/4.4.7/bits/basic_string.h:511
> No locals.
> #2  qpid::linearstore::journal::EmptyFilePool::popEmptyFile (this=0x1ab3480)
>     at /usr/src/debug/qpid-0.22/cpp/src/qpid/linearstore/journal/EmptyFilePool.cpp:213
>         l = {_sm = @0x1ab34f8}
>         emptyFileName = ""
>         isEmpty = true
> #3  0x00007ff98e59ddec in qpid::linearstore::journal::EmptyFilePool::takeEmptyFile (this=0x1ab3480,
destDirectory=
>     "/var/lib/qpidd/qls/jrnl/DurableQueue")
>     at /usr/src/debug/qpid-0.22/cpp/src/qpid/linearstore/journal/EmptyFilePool.cpp:108
>         emptyFileName = ""
>         newFileName = ""
> Expected results:
> no segfault
> Additional info:
> Relevant source code:
> std::string EmptyFilePool::popEmptyFile() {
>     std::string emptyFileName;
>     bool isEmpty = false;
>     {
>         slock l(emptyFileListMutex_);
>         isEmpty = emptyFileList_.empty();
>     }
>     if (isEmpty) {
>         createEmptyFile();
>     }
>     {
>         slock l(emptyFileListMutex_);
>         emptyFileName = emptyFileList_.front();    <-- line 213
>         emptyFileList_.pop_front();
>     }
>     return emptyFileName;
> }
> If two requests (R1 and R2) are made concurrently when EFP is empty such that:
> - R1 performs most of the function until line 212 (second lock)
>   - this means creating one empty file
> - R2 performs the same - but now EFP has one file so no new file to be created
> - R1 (or R2, it does not matter) continues on line 212 and further
>   - so it takes the empty file
> - the second request tries to take an empty file from the empty EFP and triggers the
segfault



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