diff mbox series

[2/3] um: tty: Fix handling of close in tty lines

Message ID 20201207171940.25240-2-anton.ivanov@cambridgegreys.com
State Accepted
Headers show
Series [1/3] um: Monitor error events in IRQ controller | expand

Commit Message

Anton Ivanov Dec. 7, 2020, 5:19 p.m. UTC
From: Anton Ivanov <anton.ivanov@cambridgegreys.com>

Fix a logical error in tty reading. We get 0 and errno == EAGAIN
on the first attempt to read from a closed file descriptor.

Compared to that a true EAGAIN is EAGAIN and -1.

If we check errno for EAGAIN first, before checking the return
value we miss the fact that the descriptor is closed.

This bug is as old as the driver. It was not showing up with
the original POLL based IRQ controller, because it was
producing multiple events. Switching to EPOLL unmasked it.

Fixes: ff6a17989c08 ("Epoll based IRQ controller")
Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
 arch/um/drivers/chan_user.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff mbox series


diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 4d80526a4236..d8845d4aac6a 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -26,10 +26,10 @@  int generic_read(int fd, char *c_out, void *unused)
 	n = read(fd, c_out, sizeof(*c_out));
 	if (n > 0)
 		return n;
-	else if (errno == EAGAIN)
-		return 0;
 	else if (n == 0)
 		return -EIO;
+	else if (errno == EAGAIN)
+		return 0;
 	return -errno;