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[PATCH] tty reference count fix 

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.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
hifive-unleashed-5.1
Paul Fulghum 2006-02-14 13:53:00 -08:00 committed by Linus Torvalds
parent 16bf134840
commit da965822ab
1 changed files with 3 additions and 4 deletions
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7
drivers/char/tty_io.c
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@ -1841,7 +1841,6 @@ static void release_dev(struct file * filp)
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) {
@ -1869,6 +1868,7 @@ static void release_dev(struct file * filp)
printk(KERN_WARNING "release_dev: %s: read/write wait queue "
"active!\n", tty_name(tty, buf));
up(&tty_sem);
schedule();
}
@ -1877,8 +1877,6 @@ static void release_dev(struct file * filp)
* both sides, and we've completed the last operation that could
* 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 "
@ -1892,7 +1890,6 @@ static void release_dev(struct file * filp)
tty->count, tty_name(tty, buf));
tty->count = 0;
}
up(&tty_sem);
/*
* We've decremented tty->count, so we need to remove this file
@ -1937,6 +1934,8 @@ static void release_dev(struct file * filp)
read_unlock(&tasklist_lock);
}
up(&tty_sem);
/* check whether both sides are closing ... */
if (!tty_closing || (o_tty && !o_tty_closing))
return;