#14915: T2783 fails with the threaded1 way -------------------------------------+------------------------------------- Reporter: alpmestan | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 8.5 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: x86_64 | (amd64) Type of failure: Runtime crash | Test Case: T2783 Blocked By: | Blocking: Related Tickets: #15241 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by osa1): * cc: simonmar (added) Comment: It seems to me that the assertion is wrong. Here's the stack of the TSO when we call `threadPaused()`: (the full stack is larger, only showing the relevant part here) {{{
call printStack(tso->stackobj) RET_FUN (0x7af578) (type=5) <------------------------ 0x42000060a0 stk[91] (0x42000060b0) = 0x7af578 stg_ap_pp_info <------------------------------------- 0x42000060c0 stk[88] (0x42000060c8) = 0x42000084f9 stk[87] (0x42000060d0) = 0x4200008428 NORMAL_UPDATE_FRAME(0x71da08,0x4200008428) <--------- 0x42000060d8 RET_SMALL (0x668d50) <------------------------------- 0x42000060e8 stk[83] (0x42000060f0) = 0x42000084e9 stk[82] (0x42000060f8) = 0x4200008428 NORMAL_UPDATE_FRAME(0x71da08,0x4200008428) <--------- 0x4200006100 assertion fails here ... }}}
So we have multiple update frames in this stack that updates same closure at 0x4200008428 which is originally a THUNK: {{{
call printClosure(0x4200008428) THUNK(0x404cf8) }}}
which becomes a BLACKHOLE as expected when we see it the first time in stack frame at 0x42000060d8. Then two iterations later we see the same closure in the update frame at 0x4200006100 but the assertion assumes that it's either not a BLACKHOLE or if it is then it's BLACKHOLEd by another thread. It seems to me that this assertion gives a false positive when we have a `<<loop>>` and should be updated (removed?). simonmar, am I right that this case can legitimately happen when we have a loop? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14915#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler