Cygwin: signal: Do not handle signal when __SIGFLUSHFAST is sent

The commit a22a0ad was not exactly the correct thing. Even with
the patch, some hangs still happen. This patch overrides the previous
commit togerther with the patch making cygwait() reentrant to fix these
hangs.

Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256954.html
Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256987.html
Fixes: d243e51 ("Cygwin: signal: Fix deadlock between main thread and sig thread")
Fixes: a22a0ad ("Cygwin: signal: Do not handle signal when __SIGFLUSHFAST is sent")
Reported-by: Daisuke Fujimura <[email protected]>
Reported-by: Jeremy Drake <[email protected]>
Reviewed-by:
Signed-off-by: Takashi Yano <[email protected]>

winsup/cygwin/sigproc.cc

@@ -742,6 +742,12 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       memcpy (p, si._si_commune._si_str, n); p += n;
     }
 
+  unsigned cw_mask;
+  if (pack.si.si_signo == __SIGFLUSHFAST)
+    cw_mask = 0;
+  else
+    cw_mask = cw_sig_restart;
+
   DWORD nb;
   BOOL res;
   /* Try multiple times to send if packsize != nb since that probably
@@ -751,8 +757,7 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       res = WriteFile (sendsig, leader, packsize, &nb, NULL);
       if (!res || packsize == nb)
 	break;
-      if (cygwait (NULL, 10, cw_sig_eintr) == WAIT_SIGNALED)
-	_my_tls.call_signal_handler ();
+      cygwait (NULL, 10, cw_mask);
       res = 0;
     }
 
@@ -785,7 +790,7 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
   if (wait_for_completion)
     {
       sigproc_printf ("Waiting for pack.wakeup %p", pack.wakeup);
-      rc = cygwait (pack.wakeup, WSSC);
+      rc = cygwait (pack.wakeup, WSSC, cw_mask);
       ForceCloseHandle (pack.wakeup);
     }
   else
@@ -806,9 +811,6 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       rc = -1;
     }
 
-  if (wait_for_completion && si.si_signo != __SIGFLUSHFAST)
-    _my_tls.call_signal_handler ();
-
 out:
   if (communing && rc)
     {