aboutsummaryrefslogtreecommitdiff
path: root/drivers
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2010-02-07 10:11:23 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-02-07 10:26:01 -0800
commit80e1e823989ec44d8e35bdfddadbddcffec90424 (patch)
treead6fd35a0130bc47b082135724834f7db5548c12 /drivers
parent29275254caedfedce960cfe6df24b90cb04fe431 (diff)
downloadlinux-linaro-stable-80e1e823989ec44d8e35bdfddadbddcffec90424.tar.gz
Fix race in tty_fasync() properly
This reverts commit 703625118069 ("tty: fix race in tty_fasync") and commit b04da8bfdfbb ("fnctl: f_modown should call write_lock_irqsave/ restore") that tried to fix up some of the fallout but was incomplete. It turns out that we really cannot hold 'tty->ctrl_lock' over calling __f_setown, because not only did that cause problems with interrupt disables (which the second commit fixed), it also causes a potential ABBA deadlock due to lock ordering. Thanks to Tetsuo Handa for following up on the issue, and running lockdep to show the problem. It goes roughly like this: - f_getown gets filp->f_owner.lock for reading without interrupts disabled, so an interrupt that happens while that lock is held can cause a lockdep chain from f_owner.lock -> sighand->siglock. - at the same time, the tty->ctrl_lock -> f_owner.lock chain that commit 703625118069 introduced, together with the pre-existing sighand->siglock -> tty->ctrl_lock chain means that we have a lock dependency the other way too. So instead of extending tty->ctrl_lock over the whole __f_setown() call, we now just take a reference to the 'pid' structure while holding the lock, and then release it after having done the __f_setown. That still guarantees that 'struct pid' won't go away from under us, which is all we really ever needed. Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Acked-by: Greg Kroah-Hartman <gregkh@suse.de> Acked-by: Américo Wang <xiyou.wangcong@gmail.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/char/tty_io.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index c6f3b48be9dd..dcb9083ecde0 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1951,8 +1951,10 @@ static int tty_fasync(int fd, struct file *filp, int on)
pid = task_pid(current);
type = PIDTYPE_PID;
}
- retval = __f_setown(filp, pid, type, 0);
+ get_pid(pid);
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+ retval = __f_setown(filp, pid, type, 0);
+ put_pid(pid);
if (retval)
goto out;
} else {