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SubjectRe: [vfs/tty] possible circular locking dependency detected
On Mon, 12 May 2008 20:32:59 +0200 Marcin Slusarz <marcin.slusarz@gmail.com> wrote:

> May 11 08:52:08 [kernel] [ 21.052750] Clocksource tsc unstable (delta = -109466779 ns)
> May 11 09:42:27 [kernel] [ 1104.496819] rarian-sk-get-c[5630]: segfault at 0 ip 7f478556caf0 sp 7fff8e3fe338 error 4 in libc-2.6.1.so[7f47854f9000+136000]
> May 11 10:59:48 [kernel] [ 2494.165792]
> May 11 10:59:48 [kernel] [ 2494.165794] =======================================================
> May 11 10:59:48 [kernel] [ 2494.165801] [ INFO: possible circular locking dependency detected ]
> May 11 10:59:48 [kernel] [ 2494.165805] 2.6.26-rc1-00007-g91b3a7a #217
> May 11 10:59:48 [kernel] [ 2494.165807] -------------------------------------------------------
> May 11 10:59:48 [kernel] [ 2494.165809] less/7053 is trying to acquire lock:
> May 11 10:59:48 [kernel] [ 2494.165812] (tasklist_lock){..??}, at: [<ffffffff80232e95>] is_current_pgrp_orphaned+0x15/0x50
> May 11 10:59:48 [kernel] [ 2494.165821]
> May 11 10:59:48 [kernel] [ 2494.165822] but task is already holding lock:
> May 11 10:59:48 [kernel] [ 2494.165824] (&tty->ctrl_lock){....}, at: [<ffffffff803d5f31>] tty_check_change+0x61/0x110
> May 11 10:59:48 [kernel] [ 2494.165831]
> May 11 10:59:48 [kernel] [ 2494.165832] which lock already depends on the new lock.
> May 11 10:59:48 [kernel] [ 2494.165833]
> May 11 10:59:48 [kernel] [ 2494.165835]
> May 11 10:59:48 [kernel] [ 2494.165836] the existing dependency chain (in reverse order) is:
> May 11 10:59:48 [kernel] [ 2494.165838]
> May 11 10:59:48 [kernel] [ 2494.165839] -> #2 (&tty->ctrl_lock){....}:
> May 11 10:59:48 [kernel] [ 2494.165843] [<ffffffff80253796>] __lock_acquire+0xf86/0x1080
> May 11 10:59:48 [kernel] [ 2494.165851] [<ffffffff80253922>] lock_acquire+0x92/0xc0
> May 11 10:59:48 [kernel] [ 2494.165858] [<ffffffff804deee0>] _spin_lock_irqsave+0x40/0x60
> May 11 10:59:48 [kernel] [ 2494.165866] [<ffffffff803d31b5>] __proc_set_tty+0x35/0xe0
> May 11 10:59:48 [kernel] [ 2494.165873] [<ffffffff803d76d4>] tty_ioctl+0xbf4/0xfe0
> May 11 10:59:48 [kernel] [ 2494.165880] [<ffffffff802a05e1>] vfs_ioctl+0x31/0x90
> May 11 10:59:48 [kernel] [ 2494.165888] [<ffffffff802a06b3>] do_vfs_ioctl+0x73/0x2d0
> May 11 10:59:48 [kernel] [ 2494.165895] [<ffffffff802a095a>] sys_ioctl+0x4a/0x80
> May 11 10:59:48 [kernel] [ 2494.165902] [<ffffffff8020b5ab>] system_call_after_swapgs+0x7b/0x80
> May 11 10:59:48 [kernel] [ 2494.165910] [<ffffffffffffffff>] 0xffffffffffffffff
> May 11 10:59:48 [kernel] [ 2494.165924]
> May 11 10:59:48 [kernel] [ 2494.165925] -> #1 (&sighand->siglock){++..}:
> May 11 10:59:48 [kernel] [ 2494.165929] [<ffffffff80253796>] __lock_acquire+0xf86/0x1080
> May 11 10:59:48 [kernel] [ 2494.165936] [<ffffffff80253922>] lock_acquire+0x92/0xc0
> May 11 10:59:48 [kernel] [ 2494.165943] [<ffffffff804dec1f>] _spin_lock+0x2f/0x40
> May 11 10:59:48 [kernel] [ 2494.165951] [<ffffffff8022d5a3>] copy_process+0x973/0x1210
> May 11 10:59:48 [kernel] [ 2494.165959] [<ffffffff8022df12>] do_fork+0x82/0x2f0
> May 11 10:59:48 [kernel] [ 2494.165967] [<ffffffff8020bfe1>] kernel_thread+0x81/0xde
> May 11 10:59:48 [kernel] [ 2494.165974] [<ffffffff8020c048>] child_rip+0xa/0x12
> May 11 10:59:48 [kernel] [ 2494.165981] [<ffffffffffffffff>] 0xffffffffffffffff
> May 11 10:59:48 [kernel] [ 2494.166038]
> May 11 10:59:48 [kernel] [ 2494.166039] -> #0 (tasklist_lock){..??}:
> May 11 10:59:48 [kernel] [ 2494.166043] [<ffffffff802535ab>] __lock_acquire+0xd9b/0x1080
> May 11 10:59:48 [kernel] [ 2494.166050] [<ffffffff80253922>] lock_acquire+0x92/0xc0
> May 11 10:59:48 [kernel] [ 2494.166057] [<ffffffff804dede2>] _read_lock+0x32/0x50
> May 11 10:59:48 [kernel] [ 2494.166063] [<ffffffff80232e95>] is_current_pgrp_orphaned+0x15/0x50
> May 11 10:59:48 [kernel] [ 2494.166071] [<ffffffff803d5f80>] tty_check_change+0xb0/0x110
> May 11 10:59:48 [kernel] [ 2494.166078] [<ffffffff803dac5f>] set_termios+0x1f/0x4c0
> May 11 10:59:48 [kernel] [ 2494.166085] [<ffffffff803db379>] tty_mode_ioctl+0x279/0x3e0
> May 11 10:59:48 [kernel] [ 2494.166092] [<ffffffff803db51d>] n_tty_ioctl+0x3d/0x260
> May 11 10:59:48 [kernel] [ 2494.166100] [<ffffffff803d6c34>] tty_ioctl+0x154/0xfe0
> May 11 10:59:48 [kernel] [ 2494.166107] [<ffffffff802a05e1>] vfs_ioctl+0x31/0x90
> May 11 10:59:48 [kernel] [ 2494.166114] [<ffffffff802a06b3>] do_vfs_ioctl+0x73/0x2d0
> May 11 10:59:48 [kernel] [ 2494.166121] [<ffffffff802a095a>] sys_ioctl+0x4a/0x80
> May 11 10:59:48 [kernel] [ 2494.166128] [<ffffffff8020b5ab>] system_call_after_swapgs+0x7b/0x80
> May 11 10:59:48 [kernel] [ 2494.166135] [<ffffffffffffffff>] 0xffffffffffffffff
> May 11 10:59:48 [kernel] [ 2494.166142]
> May 11 10:59:48 [kernel] [ 2494.166143] other info that might help us debug this:
> May 11 10:59:48 [kernel] [ 2494.166144]
> May 11 10:59:48 [kernel] [ 2494.166146] 1 lock held by less/7053:
> May 11 10:59:48 [kernel] [ 2494.166148] #0: (&tty->ctrl_lock){....}, at: [<ffffffff803d5f31>] tty_check_change+0x61/0x110
> May 11 10:59:48 [kernel] [ 2494.166155]
> May 11 10:59:48 [kernel] [ 2494.166156] stack backtrace:
> May 11 10:59:48 [kernel] [ 2494.166159] Pid: 7053, comm: less Not tainted 2.6.26-rc1-00007-g91b3a7a #217
> May 11 10:59:48 [kernel] [ 2494.166161]
> May 11 10:59:48 [kernel] [ 2494.166162] Call Trace:
> May 11 10:59:48 [kernel] [ 2494.166168] [<ffffffff80251223>] print_circular_bug_tail+0x83/0x90
> May 11 10:59:48 [kernel] [ 2494.166172] [<ffffffff80250889>] ? print_circular_bug_entry+0x49/0x60
> May 11 10:59:48 [kernel] [ 2494.166178] [<ffffffff802535ab>] __lock_acquire+0xd9b/0x1080
> May 11 10:59:48 [kernel] [ 2494.166184] [<ffffffff80232e95>] ? is_current_pgrp_orphaned+0x15/0x50
> May 11 10:59:48 [kernel] [ 2494.166189] [<ffffffff80253922>] lock_acquire+0x92/0xc0
> May 11 10:59:48 [kernel] [ 2494.166206] [<ffffffff803d5f80>] tty_check_change+0xb0/0x110
> May 11 10:59:48 [kernel] [ 2494.166211] [<ffffffff803dac5f>] set_termios+0x1f/0x4c0
> May 11 10:59:48 [kernel] [ 2494.166216] [<ffffffff803d3423>] ? tty_ldisc_try+0x23/0x60
> May 11 10:59:48 [kernel] [ 2494.166220] [<ffffffff803d3444>] ? tty_ldisc_try+0x44/0x60
> May 11 10:59:48 [kernel] [ 2494.166224] [<ffffffff804df2c5>] ? _spin_unlock_irqrestore+0x65/0x80
> May 11 10:59:48 [kernel] [ 2494.166230] [<ffffffff803db379>] tty_mode_ioctl+0x279/0x3e0
> May 11 10:59:48 [kernel] [ 2494.166234] [<ffffffff803d3444>] ? tty_ldisc_try+0x44/0x60
> May 11 10:59:48 [kernel] [ 2494.166239] [<ffffffff803db51d>] n_tty_ioctl+0x3d/0x260
> May 11 10:59:48 [kernel] [ 2494.166244] [<ffffffff803d6c34>] tty_ioctl+0x154/0xfe0
> May 11 10:59:48 [kernel] [ 2494.166249] [<ffffffff80252baa>] ? __lock_acquire+0x39a/0x1080
> May 11 10:59:48 [kernel] [ 2494.166256] [<ffffffff80252baa>] ? __lock_acquire+0x39a/0x1080
> May 11 10:59:48 [kernel] [ 2494.166263] [<ffffffff80252baa>] ? __lock_acquire+0x39a/0x1080
> May 11 10:59:48 [kernel] [ 2494.166269] [<ffffffff802a05e1>] vfs_ioctl+0x31/0x90
> May 11 10:59:48 [kernel] [ 2494.166274] [<ffffffff802a06b3>] do_vfs_ioctl+0x73/0x2d0
> May 11 10:59:48 [kernel] [ 2494.166280] [<ffffffff802a095a>] sys_ioctl+0x4a/0x80
> May 11 10:59:48 [kernel] [ 2494.166286] [<ffffffff8020b5ab>] system_call_after_swapgs+0x7b/0x80
> May 11 10:59:48 [kernel] [ 2494.166292]
>
> It was on 2.6.26-rc1 + some patches (afa26be86b65a7183ceac29bdf1f51d6fc6932f0)
> I think it had something to do with a hang of my yakuake (KDE terminal emulator) session.
> But I'm not sure (I noticed this warning much later)

Bummer.

I don't immediately see any reason why the ctrl_lock coverage in
tty_check_change() needs to be as broad as it is? But then it's one of
those super-secret-who-knows-what-it-does locks :( It seems to be
protecting ->session and ->pgrp.

This, perhaps...

--- a/drivers/char/tty_io.c~a
+++ a/drivers/char/tty_io.c
@@ -1215,10 +1215,11 @@ int tty_check_change(struct tty_struct *

if (!tty->pgrp) {
printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n");
- goto out;
+ goto out_unlock;
}
if (task_pgrp(current) == tty->pgrp)
- goto out;
+ goto out_unlock;
+ spin_unlock_irqrestore(&tty->ctrl_lock, flags);
if (is_ignored(SIGTTOU))
goto out;
if (is_current_pgrp_orphaned()) {
@@ -1229,6 +1230,8 @@ int tty_check_change(struct tty_struct *
set_thread_flag(TIF_SIGPENDING);
ret = -ERESTARTSYS;
out:
+ return ret;
+out_unlock:
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
return ret;
}
_


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