[PATCH] Cygwin: poll: Fix a bug on inquiring same fd with different events.

[PATCH] Cygwin: poll: Fix a bug on inquiring same fd with different events.

[Takashi Yano]

- poll() has a bug that it returns event which is not inquired if
  events are inquired in multiple pollfd entries on the same fd at
  the same time. This patch fixes the issue.
Addresses: https://cygwin.com/pipermail/cygwin/2022-June/251732.html
---
 winsup/cygwin/poll.cc       | 8 +++++---
 winsup/cygwin/release/3.3.6 | 5 +++++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/winsup/cygwin/poll.cc b/winsup/cygwin/poll.cc
index 440413433..a67507bbd 100644
--- a/winsup/cygwin/poll.cc
+++ b/winsup/cygwin/poll.cc
@@ -104,7 +104,7 @@ poll (struct pollfd *fds, nfds_t nfds, int timeout)
 	    fds[i].revents = POLLHUP;
 	  else
 	    {
-	      if (FD_ISSET(fds[i].fd, read_fds))
+	      if ((fds[i].events & POLLIN) && FD_ISSET(fds[i].fd, read_fds))
 		/* This should be sufficient for sockets, too.  Using
 		   MSG_PEEK, as before, can be considered dangerous at
 		   best.  Quote from W. Richard Stevens: "The presence
@@ -122,9 +122,11 @@ poll (struct pollfd *fds, nfds_t nfds, int timeout)
 		fds[i].revents |= (POLLIN | POLLERR);
 	      else
 		{
-		  if (FD_ISSET(fds[i].fd, write_fds))
+		  if ((fds[i].events & POLLOUT)
+		      && FD_ISSET(fds[i].fd, write_fds))
 		    fds[i].revents |= POLLOUT;
-		  if (FD_ISSET(fds[i].fd, except_fds))
+		  if ((fds[i].events & POLLPRI)
+		      && FD_ISSET(fds[i].fd, except_fds))
 		    fds[i].revents |= POLLPRI;
 		}
 	    }
diff --git a/winsup/cygwin/release/3.3.6 b/winsup/cygwin/release/3.3.6
index 49ac58ba4..f1a4b7812 100644
--- a/winsup/cygwin/release/3.3.6
+++ b/winsup/cygwin/release/3.3.6
@@ -17,3 +17,8 @@ Bug Fixes
 
 - Handle setting very long window title correctly in console.
   Addresses: https://cygwin.com/pipermail/cygwin/2022-June/251662.html
+
+- Fix a bug of poll() that it returns event which is not inquired
+  if events are inquired in multiple pollfd entries on the same fd
+  at the same time.
+  Addresses: https://cygwin.com/pipermail/cygwin/2022-June/251732.html
-- 
2.36.1

Re: [PATCH] Cygwin: poll: Fix a bug on inquiring same fd with different events.

[Ken Brown]

On 6/26/2022 9:50 PM, Takashi Yano wrote:
> - poll() has a bug that it returns event which is not inquired if
>    events are inquired in multiple pollfd entries on the same fd at
>    the same time. This patch fixes the issue.
> Addresses: https://cygwin.com/pipermail/cygwin/2022-June/251732.html

LGTM (but I haven't tested it).

Ken