Messages in this thread |  | | | Date | Sat, 12 Dec 2009 23:34:07 +0100 (CET) | | From | Thomas Gleixner <> | | Subject | Re: [GIT PATCH] TTY patches for 2.6.33-git |
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On Sat, 12 Dec 2009, Alan Cox wrote:
> > The do_tty_hangup()->tty_fasync() path takes the locks in the > > file_list_lock()->lock_kernel() direction whereas most other code takes > > them in the other direction, which cannot be good. But I'm not sure > > Thats a bug - the BKL does want to be taken first (and will > sleep/yield/drop) > > > Have a trace. I'm actually wondering if perhaps there's a missing > > unlock_kernel() somewhere else, and the tty code is just the victim of > > that. > > It's introduced by the BKL shuffle. Try the following > > > commit 1f61f07a985c7e8cfc20ad8fcced2f3d226bd0dc > Author: Alan Cox <alan@linux.intel.com> > Date: Sat Dec 12 10:32:36 2009 +0000 > > tty: Fix the AB-BA locking bug introduced in the BKL split > > The fasync path takes the BKL (it probably doesn't need to in fact) but > this causes lock inversions and deadlocks so we can't do that. Leave the > BKL over that bit for the moment. > > Identified by AKPM. > > Signed-off-by: Alan Cox <alan@linux.intel.com>
Acked-and-Tested-by: Thomas Gleixner <tglx@linutronix.de>
> diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c > index 684f0e0..f15df40 100644 > --- a/drivers/char/tty_io.c > +++ b/drivers/char/tty_io.c > @@ -516,7 +516,6 @@ static void do_tty_hangup(struct work_struct *work) > /* inuse_filps is protected by the single kernel lock */ > lock_kernel(); > check_tty_count(tty, "do_tty_hangup"); > - unlock_kernel(); > > file_list_lock(); > /* This breaks for file handles being sent over AF_UNIX sockets ? */ > @@ -531,7 +530,6 @@ static void do_tty_hangup(struct work_struct *work) > } > file_list_unlock(); > > - lock_kernel(); > tty_ldisc_hangup(tty); > > read_lock(&tasklist_lock); >
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