From 20906163a6aee2b76de240c4171928f83a5d9077 Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Wed, 28 Mar 2012 11:45:39 +0100
Subject: [PATCH] Fix a bug in threadStackOverflow() (maybe #5214)
If we overflow the current stack chunk and copy its entire contents
into the next stack chunk, we could end up with two UNDERFLOW_FRAMEs.
We had a special case to catch this in the case when the old stack
chunk was the last one (ending in STOP_FRAME), but it went wrong for
other chunks.
I found this bug while poking around in the core dump attached to
options and running the nofib suite: imaginary/wheel_sieve2 crashed
with +RTS -kc600 -kb300.
I don't know if this is the cause of all the symptoms reported in
MERGED from commit 734f1d484b12b785795b249b4116cfb4817ab55d
---
rts/Threads.c | 35 ++++++++++++++++++++++-------------
1 file changed, 22 insertions(+), 13 deletions(-)
diff --git a/rts/Threads.c b/rts/Threads.c
index 5488a320fea0..fc520c6a93fb 100644
--- a/rts/Threads.c
+++ b/rts/Threads.c
@@ -579,11 +579,6 @@ threadStackOverflow (Capability *cap, StgTSO *tso)
tso->tot_stack_size += new_stack->stack_size;
- new_stack->sp -= sizeofW(StgUnderflowFrame);
- frame = (StgUnderflowFrame*)new_stack->sp;
- frame->info = &stg_stack_underflow_frame_info;
- frame->next_chunk = old_stack;
-
{
StgWord *sp;
nat chunk_words, size;
@@ -611,6 +606,28 @@ threadStackOverflow (Capability *cap, StgTSO *tso)
sp += size;
}
+ if (sp == old_stack->stack + old_stack->stack_size) {
+ //
+ // the old stack chunk is now empty, so we do *not* insert
+ // an underflow frame pointing back to it. There are two
+ // cases: either the old stack chunk was the last one, in
+ // which case it ends with a STOP_FRAME, or it is not the
+ // last one, and it already ends with an UNDERFLOW_FRAME
+ // pointing to the previous chunk. In the latter case, we
+ // will copy the UNDERFLOW_FRAME into the new stack chunk.
+ // In both cases, the old chunk will be subsequently GC'd.
+ //
+ // With the default settings, -ki1k -kb1k, this means the
+ // first stack chunk will be discarded after the first
+ // overflow, being replaced by a non-moving 32k chunk.
+ //
+ } else {
+ new_stack->sp -= sizeofW(StgUnderflowFrame);
+ frame = (StgUnderflowFrame*)new_stack->sp;
+ frame->info = &stg_stack_underflow_frame_info;
+ frame->next_chunk = old_stack;
+ }
+
// copy the stack chunk between tso->sp and sp to
// new_tso->sp + (tso->sp - sp)
chunk_words = sp - old_stack->sp;
@@ -623,14 +640,6 @@ threadStackOverflow (Capability *cap, StgTSO *tso)
new_stack->sp -= chunk_words;
}
- // if the old stack chunk is now empty, discard it. With the
- // default settings, -ki1k -kb1k, this means the first stack chunk
- // will be discarded after the first overflow, being replaced by a
- // non-moving 32k chunk.
- if (old_stack->sp == old_stack->stack + old_stack->stack_size) {
- frame->next_chunk = (StgStack*)END_TSO_QUEUE; // dummy
- }
-
tso->stackobj = new_stack;
// we're about to run it, better mark it dirty
--
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