uml: SIGIO support cleanup

Cleanup of the SIGWINCH support.

Some code and comment reformatting.

The stack used for SIGWINCH threads was leaked.  This is now fixed by storing
it with the pid and other information, and freeing it when the thread is
killed.

If something goes wrong with a WIGWINCH thread, and this is discovered in the
interrupt handler, the winch record would leak.  It is now freed, except that
the IRQ isn't freed.  This is hard to do from interrupt context.  This has the
side-effect that the IRQ system maintains a reference to the freed structure,
but that shouldn't cause a problem since the descriptor is disabled.

register_winch_irq is now much better about cleaning up after an
initialization failure.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 38 insertions, 32 deletions

diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 5d1289d3341013..8b81bd5f20f2ff 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -51,19 +51,21 @@ error:
 /*
  * UML SIGWINCH handling
  *
- * The point of this is to handle SIGWINCH on consoles which have host ttys and
- * relay them inside UML to whatever might be running on the console and cares
- * about the window size (since SIGWINCH notifies about terminal size changes).
+ * The point of this is to handle SIGWINCH on consoles which have host
+ * ttys and relay them inside UML to whatever might be running on the
+ * console and cares about the window size (since SIGWINCH notifies
+ * about terminal size changes).
  *
- * So, we have a separate thread for each host tty attached to a UML device
- * (side-issue - I'm annoyed that one thread can't have multiple controlling
- * ttys for purposed of handling SIGWINCH, but I imagine there are other reasons
- * that doesn't make any sense).
+ * So, we have a separate thread for each host tty attached to a UML
+ * device (side-issue - I'm annoyed that one thread can't have
+ * multiple controlling ttys for the purpose of handling SIGWINCH, but
+ * I imagine there are other reasons that doesn't make any sense).
  *
- * SIGWINCH can't be received synchronously, so you have to set up to receive it
- * as a signal.  That being the case, if you are going to wait for it, it is
- * convenient to sit in sigsuspend() and wait for the signal to bounce you out of
- * it (see below for how we make sure to exit only on SIGWINCH).
+ * SIGWINCH can't be received synchronously, so you have to set up to
+ * receive it as a signal.  That being the case, if you are going to
+ * wait for it, it is convenient to sit in sigsuspend() and wait for
+ * the signal to bounce you out of it (see below for how we make sure
+ * to exit only on SIGWINCH).
  */
 
 static void winch_handler(int sig)
@@ -112,7 +114,8 @@ static int winch_thread(void *arg)
 
 	err = os_new_tty_pgrp(pty_fd, os_getpid());
 	if(err < 0){
-		printk("winch_thread : new_tty_pgrp failed, err = %d\n", -err);
+		printk("winch_thread : new_tty_pgrp failed on fd %d, "
+		       "err = %d\n", pty_fd, -err);
 		exit(1);
 	}
 
@@ -126,8 +129,9 @@ static int winch_thread(void *arg)
 		       "err = %d\n", -count);
 
 	while(1){
-		/* This will be interrupted by SIGWINCH only, since other signals
-		 * are blocked.*/
+		/* This will be interrupted by SIGWINCH only, since
+		 * other signals are blocked.
+		 */
 		sigsuspend(&sigs);
 
 		count = os_write_file(pipe_fd, &c, sizeof(c));
@@ -137,10 +141,10 @@ static int winch_thread(void *arg)
 	}
 }
 
-static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out)
+static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out,
+		       unsigned long *stack_out)
 {
 	struct winch_data data;
-	unsigned long stack;
 	int fds[2], n, err;
 	char c;
 
@@ -153,9 +157,11 @@ static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out)
 	data = ((struct winch_data) { .pty_fd 		= fd,
 				      .pipe_fd 		= fds[1] } );
 	/* CLONE_FILES so this thread doesn't hold open files which are open
-	 * now, but later closed.  This is a problem with /dev/net/tun.
+	 * now, but later closed in a different thread.  This is a
+	 * problem with /dev/net/tun, which if held open by this
+	 * thread, prevents the TUN/TAP device from being reused.
 	 */
-	err = run_helper_thread(winch_thread, &data, CLONE_FILES, &stack, 0);
+	err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out, 0);
 	if(err < 0){
 		printk("fork of winch_thread failed - errno = %d\n", -err);
 		goto out_close;
@@ -187,25 +193,25 @@ static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out)
 
 void register_winch(int fd, struct tty_struct *tty)
 {
-	int pid, thread, thread_fd = -1;
-	int count;
+	unsigned long stack;
+	int pid, thread, count, thread_fd = -1;
 	char c = 1;
 
 	if(!isatty(fd))
 		return;
 
 	pid = tcgetpgrp(fd);
-	if(!CHOOSE_MODE_PROC(is_tracer_winch, is_skas_winch, pid, fd,
-			     tty) && (pid == -1)){
-		thread = winch_tramp(fd, tty, &thread_fd);
-		if(thread > 0){
-			register_winch_irq(thread_fd, fd, thread, tty);
-
-			count = os_write_file(thread_fd, &c, sizeof(c));
-			if(count != sizeof(c))
-				printk("register_winch : failed to write "
-				       "synchronization byte, err = %d\n",
-					-count);
-		}
+	if (!CHOOSE_MODE_PROC(is_tracer_winch, is_skas_winch, pid, fd, tty) &&
+	    (pid == -1)) {
+		thread = winch_tramp(fd, tty, &thread_fd, &stack);
+		if (thread < 0)
+			return;
+
+		register_winch_irq(thread_fd, fd, thread, tty, stack);
+
+		count = os_write_file(thread_fd, &c, sizeof(c));
+		if(count != sizeof(c))
+			printk("register_winch : failed to write "
+			       "synchronization byte, err = %d\n", -count);
 	}
 }