From 13716dc35cd0869b98bd30cebbdeb8d48ab07a8b Mon Sep 17 00:00:00 2001
From: Nicholas Clark <nick@ccl4.org>
Date: Sat, 14 Apr 2012 15:51:33 +0200
Subject: [PATCH] Remove PERL_ASYNC_CHECK() from Perl_leave_scope().

PERL_ASYNC_CHECK() was added to Perl_leave_scope() as part of commit
f410a2119920dd04, which moved signal dispatch from the runloop to
control flow ops, to mitigate nearly all of the speed cost of safe
signals.

The assumption was that scope exit was a safe place to dispatch signals.
However, this is not true, as parts of the regex engine call
leave_scope(), the regex engine stores some state in per-interpreter
variables, and code called within signal handlers can change these
values.

Hence remove the call to PERL_ASYNC_CHECK() from Perl_leave_scope(), and
add it explicitly in the various OPs which were relying on their call to
leave_scope() to dispatch any pending signals. Also add a
PERL_ASYNC_CHECK() to the exit of the runloop, which ensures signals
still dispatch from S_sortcv() and S_sortcv_stacked(), as well as
addressing one of the concerns in the commit message of
f410a2119920dd04:

    Subtle bugs might remain - there might be constructions that enter
    the runloop (where signals used to be dispatched) but don't contain
    any PERL_ASYNC_CHECK() calls themselves.

Finally, move the PERL_ASYNC_CHECK(); added by that commit to pp_goto to
the end of the function, to be consistent with the positioning of all
other PERL_ASYNC_CHECK() calls - at the beginning or end of OP
functions, hence just before the return to or just after the call from
the runloop, and hence effectively at the same point as the previous
location of PERL_ASYNC_CHECK() in the runloop.
---
 dump.c   |  1 +
 pp_ctl.c | 11 ++++++++++-
 run.c    |  1 +
 scope.c  |  2 --
 4 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/dump.c b/dump.c
index b238ee0..d770a65 100644
--- a/dump.c
+++ b/dump.c
@@ -2118,6 +2118,7 @@ Perl_runops_debug(pTHX)
 	}
     } while ((PL_op = PL_op->op_ppaddr(aTHX)));
     DEBUG_l(Perl_deb(aTHX_ "leaving RUNOPS level\n"));
+    PERL_ASYNC_CHECK();
 
     TAINT_NOT;
     return 0;
diff --git a/pp_ctl.c b/pp_ctl.c
index fd92efa..6206a25 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -377,6 +377,7 @@ PP(pp_substcont)
 	    TAINT_NOT;
 	    LEAVE_SCOPE(cx->sb_oldsave);
 	    POPSUBST(cx);
+	    PERL_ASYNC_CHECK();
 	    RETURNOP(pm->op_next);
 	    /* NOTREACHED */
 	}
@@ -2732,6 +2733,7 @@ PP(pp_next)
     if (PL_scopestack_ix < inner)
 	leave_scope(PL_scopestack[PL_scopestack_ix]);
     PL_curcop = cx->blk_oldcop;
+    PERL_ASYNC_CHECK();
     return (cx)->blk_loop.my_op->op_nextop;
 }
 
@@ -2774,6 +2776,7 @@ PP(pp_redo)
     LEAVE_SCOPE(oldsave);
     FREETMPS;
     PL_curcop = cx->blk_oldcop;
+    PERL_ASYNC_CHECK();
     return redo_op;
 }
 
@@ -2978,6 +2981,7 @@ PP(pp_goto)
 		PUTBACK;
 		(void)(*CvXSUB(cv))(aTHX_ cv);
 		LEAVE;
+		PERL_ASYNC_CHECK();
 		return retop;
 	    }
 	    else {
@@ -3049,6 +3053,7 @@ PP(pp_goto)
 			}
 		    }
 		}
+		PERL_ASYNC_CHECK();
 		RETURNOP(CvSTART(cv));
 	    }
 	}
@@ -3209,6 +3214,7 @@ PP(pp_goto)
 	PL_do_undump = FALSE;
     }
 
+    PERL_ASYNC_CHECK();
     RETURNOP(retop);
 }
 
@@ -5129,10 +5135,13 @@ PP(pp_leavewhen)
 	    leave_scope(PL_scopestack[PL_scopestack_ix]);
 	PL_curcop = cx->blk_oldcop;
 
+	PERL_ASYNC_CHECK();
 	return cx->blk_loop.my_op->op_nextop;
     }
-    else
+    else {
+	PERL_ASYNC_CHECK();
 	RETURNOP(cx->blk_givwhen.leave_op);
+    }
 }
 
 PP(pp_continue)
diff --git a/run.c b/run.c
index 7c1d0aa..774852d 100644
--- a/run.c
+++ b/run.c
@@ -40,6 +40,7 @@ Perl_runops_standard(pTHX)
     register OP *op = PL_op;
     while ((PL_op = op = op->op_ppaddr(aTHX))) {
     }
+    PERL_ASYNC_CHECK();
 
     TAINT_NOT;
     return 0;
diff --git a/scope.c b/scope.c
index ffd0552..121d1f7 100644
--- a/scope.c
+++ b/scope.c
@@ -1168,8 +1168,6 @@ Perl_leave_scope(pTHX_ I32 base)
     }
 
     PL_tainted = was;
-
-    PERL_ASYNC_CHECK();
 }
 
 void
-- 
1.8.1.4