[ 
https://issues.apache.org/jira/browse/ZOOKEEPER-3885?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Tudor Bosman updated ZOOKEEPER-3885:
------------------------------------
    Description: 
We're encountering the following segfault (stack abridged).

This happens because the watcher hashtable has no locking, and is accessed 
concurrently from multiple threads:

- the thread doing zoo_aremove_watches, and
- the IO thread adding / firing watchers

We encountered this with zookeeper 3.5.8, but by code inspection the code 
appears the same in 3.6. 

```
*** Signal 11 (SIGSEGV) (0xae000000aa) received by PID 199 (pthread TID 
0x7f1d64667700) (linux TID 1273) (code: address not mapped to object), stack 
trace: ***
    @ 00007f1d98dfc8b3 folly::symbolizer::(anonymous 
namespace)::signalHandler(int, siginfo_t*, void*)
                       
/src/folly/folly/experimental/symbolizer/SignalHandler.cpp:431
    @ 00007f1d95e6c89f (unknown)
    @ 00007f1d8f73de1e containsWatcher.part.3
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zk_hashtable.c:152
    @ 00007f1d8f73e806 pathHasWatcher
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zk_hashtable.c:456
    @ 00007f1d8f7382dd aremove_watches
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zookeeper.c:4260
    @ 00007f1d8f738f82 zoo_aremove_watches
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zookeeper.c:5131
```

  was:
We're encountering the following segfault (stack abridged).

This happens because the watcher hashtable has no locking, and is accessed 
concurrently from multiple threads:

- the thread doing zoo_aremove_watches, and
- the IO thread adding / firing watchers

We encountered this with zookeeper 3.5.8, but by code inspection the code 
appears the same in 3.6. 

*** Signal 11 (SIGSEGV) (0xae000000aa) received by PID 199 (pthread TID 
0x7f1d64667700) (linux TID 1273) (code: address not mapped to object), stack 
trace: ***
    @ 00007f1d98dfc8b3 folly::symbolizer::(anonymous 
namespace)::signalHandler(int, siginfo_t*, void*)
                       
/src/folly/folly/experimental/symbolizer/SignalHandler.cpp:431
    @ 00007f1d95e6c89f (unknown)
    @ 00007f1d8f73de1e containsWatcher.part.3
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zk_hashtable.c:152
    @ 00007f1d8f73e806 pathHasWatcher
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zk_hashtable.c:456
    @ 00007f1d8f7382dd aremove_watches
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zookeeper.c:4260
    @ 00007f1d8f738f82 zoo_aremove_watches
                       
/src/zookeeper/zookeeper-client/zookeeper-client-c/src/zookeeper.c:5131



> zoo_aremove_watches segfault: zk_hashtable needs locking!
> ---------------------------------------------------------
>
>                 Key: ZOOKEEPER-3885
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3885
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: c client
>    Affects Versions: 3.6.1, 3.5.8
>            Reporter: Tudor Bosman
>            Priority: Major
>
> We're encountering the following segfault (stack abridged).
> This happens because the watcher hashtable has no locking, and is accessed 
> concurrently from multiple threads:
> - the thread doing zoo_aremove_watches, and
> - the IO thread adding / firing watchers
> We encountered this with zookeeper 3.5.8, but by code inspection the code 
> appears the same in 3.6. 
> ```
> *** Signal 11 (SIGSEGV) (0xae000000aa) received by PID 199 (pthread TID 
> 0x7f1d64667700) (linux TID 1273) (code: address not mapped to object), stack 
> trace: ***
>     @ 00007f1d98dfc8b3 folly::symbolizer::(anonymous 
> namespace)::signalHandler(int, siginfo_t*, void*)
>                        
> /src/folly/folly/experimental/symbolizer/SignalHandler.cpp:431
>     @ 00007f1d95e6c89f (unknown)
>     @ 00007f1d8f73de1e containsWatcher.part.3
>                        
> /src/zookeeper/zookeeper-client/zookeeper-client-c/src/zk_hashtable.c:152
>     @ 00007f1d8f73e806 pathHasWatcher
>                        
> /src/zookeeper/zookeeper-client/zookeeper-client-c/src/zk_hashtable.c:456
>     @ 00007f1d8f7382dd aremove_watches
>                        
> /src/zookeeper/zookeeper-client/zookeeper-client-c/src/zookeeper.c:4260
>     @ 00007f1d8f738f82 zoo_aremove_watches
>                        
> /src/zookeeper/zookeeper-client/zookeeper-client-c/src/zookeeper.c:5131
> ```



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