Messages in this thread Patch in this message | | | Date | Mon, 13 Feb 2006 17:51:41 -0500 (EST) | From | Jason Baron <> | Subject | Re: [PATCH] tty reference count fix |
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On Mon, 13 Feb 2006, Paul Fulghum wrote:
> Fix hole where tty structure can be released when reference > count is non zero. Existing code can sleep without tty_sem > protection between deciding to release the tty structure > (setting local variables tty_closing and otty_closing) > and setting TTY_CLOSING to prevent further opens. > An open can occur during this interval causing release_dev() > to free the tty structure while it is still referenced. > > This should fix bugzilla.kernel.org > [Bug 6041] New: Unable to handle kernel paging request > > In Bug 6041, tty_open() oopes on accessing the tty structure > it has successfully claimed. Bug was on SMP machine > with the same tty being opened and closed by > multiple processes, and DEBUG_PAGEALLOC enabled. >
patch looks good to me. Or you could even drop the tty_sem completely from the release_dev path (patch below) since lock_kernel() is held in both tty_open() and the release_dev paths() (and there is no sleeping b/w setting the tty_closing flag and setting the TTY_CLOSING bit).
-Jason
Signed-off-by: Jason Baron <jbaron@redhat.com>
--- linux-2.6-working/drivers/char/tty_io.c.bak +++ linux-2.6-working/drivers/char/tty_io.c @@ -1829,14 +1829,9 @@ static void release_dev(struct file * fi * each iteration we avoid any problems. */ while (1) { - /* Guard against races with tty->count changes elsewhere and - opens on /dev/tty */ - - down(&tty_sem); tty_closing = tty->count <= 1; o_tty_closing = o_tty && (o_tty->count <= (pty_master ? 1 : 0)); - up(&tty_sem); do_sleep = 0; if (tty_closing) { @@ -1873,7 +1868,6 @@ static void release_dev(struct file * fi * block, so it's safe to proceed with closing. */ - down(&tty_sem); if (pty_master) { if (--o_tty->count < 0) { printk(KERN_WARNING "release_dev: bad pty slave count " @@ -1887,7 +1881,6 @@ static void release_dev(struct file * fi tty->count, tty_name(tty, buf)); tty->count = 0; } - up(&tty_sem); /* * We've decremented tty->count, so we need to remove this file - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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