[GHC] #13970: Segmentation fault inside threadPaused

[GHC]

#13970: Segmentation fault inside threadPaused
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        Reporter:  albertov          |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Runtime System    |              Version:  8.2.1-rc3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"bade356f79d44c9f6e8918a89d9ffac7f5608dbf/ghc" bade356/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="bade356f79d44c9f6e8918a89d9ffac7f5608dbf"
 rts: Claim AP_STACK before adjusting Sp

 In the fix to #13615 we introduced some logic to atomically blackhole
 AP_STACKs closures upon entry. However, this logic was placed *after* a
 stack pointer adjustment. This meant that if someone else beat us to
 blackholing the AP_STACK we would suspend the thread with uninitialized
 content on the stack.  This would then later blow up when threadPaused
 attempted to walk the stack, hence #13970.

 Silly bug but still cost lots of head-scratching to find.

 Thanks to albertov for the great repro.

 Fixes #13970. Bug originally introduced by the fix to #13615.

 Reviewers: austin, erikd, simonmar

 Reviewed By: erikd, simonmar

 Subscribers: rwbarton, thomie

 GHC Trac Issues: #13970, #13615

 Differential Revision: https://phabricator.haskell.org/D3760
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13970#comment:27>
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