[PATCH 3/6] Cygwin: signal: Cleanup signal queue after processing it

[Takashi Yano]

The queue is once cleaned-up, however, sigpacket::process() may set
si_signo in the queue to 0 by calling sig_clear(). This patch adds
another loop for cleanup after calling sigpacket::process().

Addresses: https://cygwin.com/pipermail/cygwin/2024-November/256744.html
Fixes: 9d2155089e87 ("(wait_sig): Define variable q to be the start of the signal queue.  Just iterate through sigq queue, deleting processed or zeroed signals")
Reported-by: Christian Franke <Christian.Franke@t-online.de>
Reviewed-by:
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
---
 winsup/cygwin/sigproc.cc | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
index 34e459070..541f90cb7 100644
--- a/winsup/cygwin/sigproc.cc
+++ b/winsup/cygwin/sigproc.cc
@@ -1471,6 +1471,17 @@ wait_sig (VOID *)
 		      qnext->si.si_signo = 0;
 		    }
 		}
+	      /* Cleanup sigq chain. Remove entries having si_signo == 0.
+		 There were once cleaned obeve, however sigpacket::process()
+		 may set si_signo to 0 using sig_clear(). */
+	      q = &sigq.start;
+	      while ((qnext = q->next))
+		{
+		  if (qnext->si.si_signo)
+		    q = qnext;
+		  else
+		    q->next = qnext->next;
+		}
 	      /* At least one signal still queued?  The event is used in select
 		 only, and only to decide if WFMO should wake up in case a
 		 signalfd is waiting via select/poll for being ready to read a
-- 
2.45.1