Previously, a deadlock happened if many SIGSTOP/SIGCONT signals were received rapidly. If the main thread sends __SIGFLUSH at the timing when SIGSTOP is handled by the sig thread, but not is handled by the main thread yet (sig_handle_tty_stop() not called yet), and if SIGCONT is received, the sig thread waits for cygtls::current_sig (is SIGSTOP now) cleared. However, the main thread waits for the pack.wakeup using WaitForSingleObject(), so the main thread cannot handle SIGSTOP. This is the mechanism of the deadlock. This patch uses cygwait() instead of WaitForSingleObject() to be able to handle the pending SIGSTOP.
Addresses: https://cygwin.com/pipermail/cygwin/2024-November/256744.html Fixes: 7759daa979c4 ("(sig_send): Fill out sigpacket structure to send to signal thread rather than racily sending separate packets.") Reported-by: Christian Franke <christian.fra...@t-online.de> Reviewed-by: Signed-off-by: Takashi Yano <takashi.y...@nifty.ne.jp> --- winsup/cygwin/sigproc.cc | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc index 81b6c3169..b67eccf4d 100644 --- a/winsup/cygwin/sigproc.cc +++ b/winsup/cygwin/sigproc.cc @@ -760,7 +760,7 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls) if (wait_for_completion) { sigproc_printf ("Waiting for pack.wakeup %p", pack.wakeup); - rc = WaitForSingleObject (pack.wakeup, WSSC); + rc = cygwait (pack.wakeup, WSSC); ForceCloseHandle (pack.wakeup); } else -- 2.45.1
