#4850: Segfault when lots of blocked MVar messages
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Reporter: NeilMitchell | Owner:
Type: bug | Status: merge
Priority: high | Milestone: 7.0.2
Component: Runtime System | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Windows | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime crash
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Changes (by simonmar):
* status: new => merge
* milestone: 7.0.3 => 7.0.2
Comment:
Fixed:
{{{
Tue Dec 21 11:49:11 GMT 2010 Simon Marlow <[email protected]>
* releaseCapabilityAndQueueWorker: task->stopped should be false (#4850)
Tue Dec 21 11:58:07 GMT 2010 Simon Marlow <[email protected]>
* boundTaskExiting: don't set task->stopped unless this is the last call
(#4850)
The bug in this case was that we had a worker thread making a foreign
call which invoked a callback (in this case it was performGC, I
think). When the callback ended, boundTaskExiting() was setting
task->stopped, but the Task is now per-OS-thread, so it is shared by
the worker that made the original foreign call. When the foreign call
returned, because task->stopped was set, the worker was not placed on
the queue of spare workers. Somehow the worker woke up again, and
found the spare_workers queue empty, which lead to a crash.
Two bugs here: task->stopped should not have been set by
boundTaskExiting (this broke when I split the Task and InCall structs,
in 6.12.2), and releaseCapabilityAndQueueWorker() should not be
testing task->stopped anyway, because it should only ever be called
when task->stopped is false (this is now an assertion).
}}}
We should get this in 7.0.2.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4850#comment:2>
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