diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2010-02-07 10:11:23 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-04-01 15:55:43 -0700 |
| commit | c89094b689c85b9e6c2fcf97e0c7d81620e46f79 (patch) | |
| tree | 30965436fa841347b6968f1b0cd73f04f592067b | |
| parent | 51d5fe4109bff13686634a408988547e2d1b3add (diff) | |
Fix race in tty_fasync() properly
commit 80e1e823989ec44d8e35bdfddadbddcffec90424 upstream.
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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
| -rw-r--r-- | drivers/char/tty_io.c | 4 | ||||
| -rw-r--r-- | fs/fcntl.c | 6 |
2 files changed, 5 insertions, 5 deletions
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c index c695ce7985e0..9531cf8b3482 100644 --- a/drivers/char/tty_io.c +++ b/drivers/char/tty_io.c @@ -1912,8 +1912,10 @@ 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 { diff --git a/fs/fcntl.c b/fs/fcntl.c index 926e75394da1..11fd78c4b07e 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -199,9 +199,7 @@ static int setfl(int fd, struct file * filp, unsigned long arg) static void f_modown(struct file *filp, struct pid *pid, enum pid_type type, int force) { - unsigned long flags; - - write_lock_irqsave(&filp->f_owner.lock, flags); + write_lock_irq(&filp->f_owner.lock); if (force || !filp->f_owner.pid) { put_pid(filp->f_owner.pid); filp->f_owner.pid = get_pid(pid); @@ -213,7 +211,7 @@ static void f_modown(struct file *filp, struct pid *pid, enum pid_type type, filp->f_owner.euid = cred->euid; } } - write_unlock_irqrestore(&filp->f_owner.lock, flags); + write_unlock_irq(&filp->f_owner.lock); } int __f_setown(struct file *filp, struct pid *pid, enum pid_type type, |