On Tue, Feb 22, 2011 at 12:02:22PM -0800, Greg KH wrote: > On Tue, Feb 22, 2011 at 09:15:47AM +0800, Daniel J Blueman wrote: > > On 22 February 2011 00:25, Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote: > > > On Tue, 2011-02-22 at 00:11 +0800, Daniel J Blueman wrote: > > >> I previously managed to reproduce a hang while scanning wireless > > >> channels (reproducible with airodump-ng hopping channels); subsequent > > >> lockdep instrumentation revealed a lock ordering issue [1]. > > >> > > >> Without knowing the design intent, it looks like the locks should be > > >> taken in reverse order; please comment. > > >> > > >> Signed-off-by: Daniel J Blueman <daniel.blueman@xxxxxxxxx> > > >> > > >> --- [1] > > > > > > Yeah, looks this way, thanks. > > > > > > Acked-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx> > > > > > >> ======================================================= > > >> [ INFO: possible circular locking dependency detected ] > > >> 2.6.38-rc5-341cd #4 > > >> ------------------------------------------------------- > > >> airodump-ng/15445 is trying to acquire lock: > > >> (&rdev->devlist_mtx){+.+.+.}, at: [<ffffffff816b1266>] > > >> cfg80211_wext_siwfreq+0xc6/0x100 > > >> > > >> but task is already holding lock: > > >> (&wdev->mtx){+.+.+.}, at: [<ffffffff816b125c>] cfg80211_wext_siwfreq+0xbc/0x100 > > >> > > >> which lock already depends on the new lock. > > >> > > >> the existing dependency chain (in reverse order) is: > > >> > > >> -> #1 (&wdev->mtx){+.+.+.}: > > >> [<ffffffff810a79d6>] lock_acquire+0xc6/0x280 > > >> [<ffffffff816d6bce>] mutex_lock_nested+0x6e/0x4b0 > > >> [<ffffffff81696080>] cfg80211_netdev_notifier_call+0x430/0x5f0 > > >> [<ffffffff8109351b>] notifier_call_chain+0x8b/0x100 > > >> [<ffffffff810935b1>] raw_notifier_call_chain+0x11/0x20 > > >> [<ffffffff81576d92>] call_netdevice_notifiers+0x32/0x60 > > >> [<ffffffff815771a4>] __dev_notify_flags+0x34/0x80 > > >> [<ffffffff81577230>] dev_change_flags+0x40/0x70 > > >> [<ffffffff8158587c>] do_setlink+0x1fc/0x8d0 > > >> [<ffffffff81586042>] rtnl_setlink+0xf2/0x140 > > >> [<ffffffff81586923>] rtnetlink_rcv_msg+0x163/0x270 > > >> [<ffffffff8159d741>] netlink_rcv_skb+0xa1/0xd0 > > >> [<ffffffff815867b0>] rtnetlink_rcv+0x20/0x30 > > >> [<ffffffff8159d39a>] netlink_unicast+0x2ba/0x300 > > >> [<ffffffff8159dd57>] netlink_sendmsg+0x267/0x3e0 > > >> [<ffffffff8155e364>] sock_sendmsg+0xe4/0x110 > > >> [<ffffffff8155f3a3>] sys_sendmsg+0x253/0x3b0 > > >> [<ffffffff81003192>] system_call_fastpath+0x16/0x1b > > >> > > >> -> #0 (&rdev->devlist_mtx){+.+.+.}: > > >> [<ffffffff810a7222>] __lock_acquire+0x1622/0x1d10 > > >> [<ffffffff810a79d6>] lock_acquire+0xc6/0x280 > > >> [<ffffffff816d6bce>] mutex_lock_nested+0x6e/0x4b0 > > >> [<ffffffff816b1266>] cfg80211_wext_siwfreq+0xc6/0x100 > > >> [<ffffffff816b2fad>] ioctl_standard_call+0x5d/0xd0 > > >> [<ffffffff816b3223>] T.808+0x163/0x170 > > >> [<ffffffff816b326a>] wext_handle_ioctl+0x3a/0x90 > > >> [<ffffffff815798d2>] dev_ioctl+0x6f2/0x830 > > >> [<ffffffff8155cf3d>] sock_ioctl+0xfd/0x290 > > >> [<ffffffff8117dffd>] do_vfs_ioctl+0x9d/0x590 > > >> [<ffffffff8117e53a>] sys_ioctl+0x4a/0x80 > > >> [<ffffffff81003192>] system_call_fastpath+0x16/0x1b > > >> > > >> other info that might help us debug this: > > >> > > >> 2 locks held by airodump-ng/15445: > > >> #0: (rtnl_mutex){+.+.+.}, at: [<ffffffff81586782>] rtnl_lock+0x12/0x20 > > >> #1: (&wdev->mtx){+.+.+.}, at: [<ffffffff816b125c>] > > >> cfg80211_wext_siwfreq+0xbc/0x100 > > >> > > >> stack backtrace: > > >> Pid: 15445, comm: airodump-ng Not tainted 2.6.38-rc5-341cd #4 > > >> Call Trace: > > >> [<ffffffff810a3f0a>] ? print_circular_bug+0xfa/0x100 > > >> [<ffffffff810a7222>] ? __lock_acquire+0x1622/0x1d10 > > >> [<ffffffff810a1f99>] ? trace_hardirqs_off_caller+0x29/0xc0 > > >> [<ffffffff810a79d6>] ? lock_acquire+0xc6/0x280 > > >> [<ffffffff816b1266>] ? cfg80211_wext_siwfreq+0xc6/0x100 > > >> [<ffffffff810a31d7>] ? mark_held_locks+0x67/0x90 > > >> [<ffffffff816d6bce>] ? mutex_lock_nested+0x6e/0x4b0 > > >> [<ffffffff816b1266>] ? cfg80211_wext_siwfreq+0xc6/0x100 > > >> [<ffffffff810a31d7>] ? mark_held_locks+0x67/0x90 > > >> [<ffffffff816b1266>] ? cfg80211_wext_siwfreq+0xc6/0x100 > > >> [<ffffffff816b1266>] ? cfg80211_wext_siwfreq+0xc6/0x100 > > >> [<ffffffff816b2fad>] ? ioctl_standard_call+0x5d/0xd0 > > >> [<ffffffff8157818b>] ? __dev_get_by_name+0x9b/0xc0 > > >> [<ffffffff816b2f50>] ? ioctl_standard_call+0x0/0xd0 > > >> [<ffffffff816b3223>] ? T.808+0x163/0x170 > > >> [<ffffffff8112ddf2>] ? might_fault+0x72/0xd0 > > >> [<ffffffff816b326a>] ? wext_handle_ioctl+0x3a/0x90 > > >> [<ffffffff8112de3b>] ? might_fault+0xbb/0xd0 > > >> [<ffffffff815798d2>] ? dev_ioctl+0x6f2/0x830 > > >> [<ffffffff810a1bae>] ? put_lock_stats+0xe/0x40 > > >> [<ffffffff810a1c8c>] ? lock_release_holdtime+0xac/0x150 > > >> [<ffffffff8155cf3d>] ? sock_ioctl+0xfd/0x290 > > >> [<ffffffff8117dffd>] ? do_vfs_ioctl+0x9d/0x590 > > >> [<ffffffff8116c8ff>] ? fget_light+0x1df/0x3c0 > > >> [<ffffffff8117e53a>] ? sys_ioctl+0x4a/0x80 > > >> [<ffffffff81003192>] ? system_call_fastpath+0x16/0x1b > > >> > > >> --- [2] > > >> > > >> diff --git a/net/wireless/wext-compat.c b/net/wireless/wext-compat.c > > >> index 3e5dbd4..d112f03 100644 > > >> --- a/net/wireless/wext-compat.c > > >> +++ b/net/wireless/wext-compat.c > > >> @@ -802,11 +802,11 @@ int cfg80211_wext_siwfreq(struct net_device *dev, > > >> return freq; > > >> if (freq == 0) > > >> return -EINVAL; > > >> - wdev_lock(wdev); > > >> mutex_lock(&rdev->devlist_mtx); > > >> + wdev_lock(wdev); > > >> err = cfg80211_set_freq(rdev, wdev, freq, NL80211_CHAN_NO_HT); > > >> - mutex_unlock(&rdev->devlist_mtx); > > >> wdev_unlock(wdev); > > >> + mutex_unlock(&rdev->devlist_mtx); > > >> return err; > > >> default: > > >> return -EOPNOTSUPP; > > > > Please consider for -stable. This patch resolves the lock ordering > > case my test exposed, and passes lockdep and extended testing. > > Consider what? What is the git commit id of this patch in Linus's tree? I just sent this to Dave M. The commit id should be 4f919a3bc54da01db829c520ce4b1fabfde1c3f7 when it hits Linus' tree. Hth! John -- John W. Linville Someday the world will need a hero, and you linville@xxxxxxxxxxxxx might be all we have. Be ready. -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html