[GHC] #15608: Segfault in retainer profiling

[GHC]

#15608: Segfault in retainer profiling
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        Reporter:  osa1              |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Profiling         |              Version:  8.5
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D5134
       Wiki Page:                    |
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Comment (by osa1):

 One of the problems is that because of recursive `retainClosure()` calls
 retainer profiler sometimes fills the C stack. I currently see 14000+
 stack frames because of this loop:

 {{{
 #174645 retainClosure
     (c0=<optimized out>, cp0=cp0 at entry=0x4201ecaa20, r0=r0 at entry=0x6810bc0
 <CCS_SYSTEM>)
     at rts/RetainerProfile.c:1598

 #174646 0x00000000059b48c7 in retain_small_bitmap
     (c_child_r=<optimized out>, c=0x4201ecaa20, bitmap=0, size=<optimized
 out>, p=0x4201ecaa50)
     at rts/RetainerProfile.c:1140

 #174647 retain_PAP_payload
     (n_args=<optimized out>, payload=0x4201ecaa50, fun=<optimized out>,
 c_child_r=<optimized out>, pap=0x4201ecaa20)
     at rts/RetainerProfile.c:1334

 #174648 retainClosure
     (c0=<optimized out>, cp0=cp0 at entry=0x4203affe88, r0=r0 at entry=0x6810bc0
 <CCS_SYSTEM>)
     at rts/RetainerProfile.c:1598
 }}}

 I don't understand how retainer profiler works yet. It has a stack, and a
 maxStack variable, but I don't understand why we sometimes push work to
 the stack and sometimes recurse, and maxStack seems to be unused.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15608#comment:3>
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