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Commit ed1b58d8 authored by Bodo Stroesser's avatar Bodo Stroesser Committed by Linus Torvalds
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[PATCH] uml: fix SIGWINCH handler race while waiting for signals. 



If a SIGWINCH comes in, while winch_thread() isn't waiting in wait(),
winch_thread could miss signals.  It isn't very probable, that anyone will
see this causing trouble, as it would need a very special timing, that a
missed SIGWINCH results in a wrong window size.

So, this is a minor problem.  But why not fix, as it can be done so easy?

Signed-off-by: default avatarBodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: default avatarPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 02215759

arch/um/drivers/chan_user.c

+6 −5
Original line number Diff line number Diff line
@@ -63,7 +63,7 @@ int generic_console_write(int fd, const char *buf, int n, void *unused) 
 *

 * 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 a pause() and wait for the signal to bounce you out of

 * 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).

 */
@@ -94,18 +94,19 @@ static int winch_thread(void *arg) 
		       "byte, err = %d\n", -count);



	/* We are not using SIG_IGN on purpose, so don't fix it as I thought to

	 * do! If using SIG_IGN, the pause() call below would not stop on

	 * do! If using SIG_IGN, the sigsuspend() call below would not stop on

	 * SIGWINCH. */



	signal(SIGWINCH, winch_handler);

	sigfillset(&sigs);

	sigdelset(&sigs, SIGWINCH);

	/* Block anything else than SIGWINCH. */

	/* Block all signals possible. */

	if(sigprocmask(SIG_SETMASK, &sigs, NULL) < 0){

		printk("winch_thread : sigprocmask failed, errno = %d\n", 

		       errno);

		exit(1);

	}

	/* In sigsuspend(), block anything else than SIGWINCH. */

	sigdelset(&sigs, SIGWINCH);



	if(setsid() < 0){

		printk("winch_thread : setsid failed, errno = %d\n", errno);
@@ -130,7 +131,7 @@ static int winch_thread(void *arg) 
	while(1){

		/* This will be interrupted by SIGWINCH only, since other signals

		 * are blocked.*/

		pause();

		sigsuspend(&sigs);



		count = os_write_file(pipe_fd, &c, sizeof(c));

		if(count != sizeof(c))