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SubjectRe: [2.6.33-rc5] tty: possible irq lock inversion dependency in tty_fasync


On Sat, 6 Feb 2010, Linus Torvalds wrote:
>
> Yeah. I think we need to just revert that commit.
>
> Or maybe we could just do the following, rather than revert it outright:
> just get a ref to the 'struct pid' while holding the spinlock, and then
> releasing it after doing the __f_setown() call.

Btw, if we do this, then we should probably revert commit
b04da8bfdfbbd79544cab2fadfdc12e87eb01600 at the same time.

Resulting patch would then look like the appended.

Linus

---
drivers/char/tty_io.c | 4 +++-
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 c6f3b48..dcb9083 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 {
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 5ef953e..97e01dc 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,

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