If SIGCONT starts processing while __SIGFLUSHFAST is ongoing, _main_tls->current_sig will never be cleared because the signal processing is stopped while waiting for the wake-up event in the main thread. This leads to a deadlock in the while loop waiting for current_sig to be cleared. With this patch, the function returns to wait_sig() if current_sig is set, rather than waiting for it in the while loop.
Addresses: https://cygwin.com/pipermail/cygwin/2025-February/257473.html Fixes: 9d2155089e87 ("(sigpacket::process): Call handle_SIGCONT early to deal with SIGCONT.") Reported-by: Christian Franke <christian.fra...@t-online.de> Reviewed-by: Signed-off-by: Takashi Yano <takashi.y...@nifty.ne.jp> --- winsup/cygwin/exceptions.cc | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc index f576c5ff2..c6e82b6c5 100644 --- a/winsup/cygwin/exceptions.cc +++ b/winsup/cygwin/exceptions.cc @@ -1425,23 +1425,18 @@ _cygtls::handle_SIGCONT () if (NOTSTATE (myself, PID_STOPPED)) return; - myself->stopsig = 0; - myself->process_state &= ~PID_STOPPED; - /* Carefully tell sig_handle_tty_stop to wake up. - Make sure that any pending signal is handled before trying to - send a new one. Then make sure that SIGCONT has been recognized - before exiting the loop. */ - while (current_sig) /* Assume that it's ok to just test sig outside of a */ - yield (); /* lock since setup_handler does it this way. */ - lock (); current_sig = SIGCONT; set_signal_arrived (); /* alert sig_handle_tty_stop */ unlock (); + /* Make sure that SIGCONT has been recognized before exiting the loop. */ while (current_sig == SIGCONT) yield (); + myself->stopsig = 0; + myself->process_state &= ~PID_STOPPED; + /* Clear pending stop signals */ sig_clear (SIGSTOP, false); sig_clear (SIGTSTP, false); @@ -1473,7 +1468,17 @@ sigpacket::process () myself->rusage_self.ru_nsignals++; if (si.si_signo == SIGCONT) - _main_tls->handle_SIGCONT (); + { + /* Carefully tell sig_handle_tty_stop to wake up. + Make sure that any pending signal is handled before trying to + send a new one. */ + if (_main_tls->current_sig) + { + rc = -1; + goto done; + } + _main_tls->handle_SIGCONT (); + } /* SIGKILL is special. It always goes through. */ if (si.si_signo == SIGKILL) -- 2.45.1
