Date:	Wed, 16 May 2007 12:09:56 -0700
From:	"Ray Lee" <ray-lk@...rabbit.org>
To:	"Satyam Sharma" <satyam.sharma@...il.com>
Cc:	"Alan Stern" <stern@...land.harvard.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	"Max Krasnyansky" <maxk@...lcomm.com>, marcel@...tmann.org,
	bluez-devel@...ts.sf.net
Subject: Re: [PATCH] make hci_notifier a blocking notifier (was Re: BUG: sleeping function called from invalid context at net/core/sock.c:1523)

Apologies for taking so long to get back to you -- I've been on the
road for the last week and have finally got to a point where I could
test the patch.

On 5/6/07, Satyam Sharma <satyam.sharma@...il.com> wrote:
> (Dropped Pavel, Rafael and linux-pm from CC list, this isn't a PM
> error so don't want to spam them; and added bluez-devel)
>
> On 5/7/07, Ray Lee <ray-lk@...rabbit.org> wrote:
> > On 5/6/07, Alan Stern <stern@...land.harvard.edu> wrote:
> > > On Sun, 6 May 2007, Satyam Sharma wrote:
> > >
> > > > Anyway, the hci_notifier is called from the following six call sites:
> > > >
> > > > hci_dev_open() and hci_dev_close() -> both called from
> > > > hci_sock_ioctl() => both can sleep
> > > > hci_register_dev() and hci_unregister_dev() => again both are capable
> > > > of sleeping
> > > > hci_suspend_dev() and hci_resume_dev() -> called from the .suspend()
> > > > and .resume() of the hci_usb_driver, and again both of these can sleep
> > > >
> > > > Is there any other reason why hci_notifier must be an atomic notifier?
> > > >
> > > > (CC'ing Alan Stern just in case, apparently hci_notifier became atomic
> > > > when notifier chains were classified into atomic / blocking)
> > >
> > > I don't remember exactly why this particular choice was made.  Perhaps we
> > > found that the notifier callout routines didn't use any blocking
> > > primitives (we may have been mistaken about this -- there was a lot of
> > > code to check) and so therefore the choice didn't matter.  In that case we
> > > probably just decided to make it an atomic notifier to keep things simple.
> > >
> > > As you found, changing it to a blocking notifier is very easy.  Provided
> > > all the callers are non-atomic it should work just fine.
> >
> > Okay, I'll go ahead and try the patch, then, and report back.
>
> You'd still get the BUG message. To fully resolve the problem, we need
> to make the hci_sock_dev_event() notifier callout blocking (which
> happened with this patch) but also convert hci_sk_list.lock to a
> rwsem, but some users of that rwlock (other than hci_sock_dev_event)
> are atomic.
>
> However, please do try and get back, as your testing would still be
> helpful to see whether converting hci_notifier to blocking had other
> side-effects -- if you only see the same message again and otherwise
> things seem fine, then we're good as far as at least this change was
> concerned.

Yes, it's roughly the same trace. There are some differences, though
those are likely due to me finding a new way to trigger the issue. (My
laptop has a button to turn the WiFi/Bluetooth on and off. Hitting
that and causing a disconnect of the internal Bluetooth connector
triggers the same issue without going through a suspend/resume cycle.)

[  272.539154] BUG: sleeping function called from invalid context at
net/core/sock.c:1547
[  272.539161] in_atomic():1, irqs_disabled():0
[  272.539163] 2 locks held by khubd/1350:
[  272.539165]  #0:  ((hci_notifier).rwsem){----}, at:
[<ffffffff8023741b>] __blocking_notifier_call_chain+0x3b/0x80
[  272.539175]  #1:  (old_style_rw_init#2){-.-?}, at:
[<ffffffff88203c53>] hci_sock_dev_event+0x53/0x100 [bluetooth]
[  272.539196]
[  272.539197] Call Trace:
[  272.539203]  [<ffffffff80245833>] debug_show_held_locks+0x13/0x30
[  272.539216]  [<ffffffff80224963>] __might_sleep+0xc3/0xf0
[  272.539221]  [<ffffffff803c29dc>] lock_sock_nested+0x2c/0x120
[  272.539231]  [<ffffffff88203c53>] :bluetooth:hci_sock_dev_event+0x53/0x100
[  272.539241]  [<ffffffff88203c76>] :bluetooth:hci_sock_dev_event+0x76/0x100
[  272.539250]  [<ffffffff8045d073>] notifier_call_chain+0x53/0x80
[  272.539256]  [<ffffffff80237431>] __blocking_notifier_call_chain+0x51/0x80
[  272.539262]  [<ffffffff80237471>] blocking_notifier_call_chain+0x11/0x20
[  272.539270]  [<ffffffff881fed16>] :bluetooth:hci_notify+0x16/0x20
[  272.539278]  [<ffffffff881ffdbb>] :bluetooth:hci_unregister_dev+0x5b/0x80
[  272.539286]  [<ffffffff88224136>] :hci_usb:hci_usb_disconnect+0x56/0x90
[  272.539309]  [<ffffffff8801e66e>] :usbcore:usb_unbind_interface+0x4e/0xa0
[  272.539315]  [<ffffffff80380d86>] __device_release_driver+0x86/0xc0
[  272.539320]  [<ffffffff803812e6>] device_release_driver+0x46/0x70
[  272.539325]  [<ffffffff803804e3>] bus_remove_device+0x63/0x90
[  272.539329]  [<ffffffff8037e474>] device_del+0x1a4/0x2e0
[  272.539344]  [<ffffffff8801b8c6>] :usbcore:usb_disable_device+0x96/0x120
[  272.539358]  [<ffffffff880173ba>] :usbcore:usb_disconnect+0xba/0x140
[  272.539372]  [<ffffffff88017ac3>] :usbcore:hub_thread+0x263/0xdb0
[  272.539382]  [<ffffffff80456b66>] __sched_text_start+0x296/0x2ce
[  272.539389]  [<ffffffff8023eb30>] autoremove_wake_function+0x0/0x40
[  272.539403]  [<ffffffff88017860>] :usbcore:hub_thread+0x0/0xdb0
[  272.539408]  [<ffffffff8023e73d>] kthread+0x4d/0x80
[  272.539414]  [<ffffffff8020a298>] child_rip+0xa/0x12
[  272.539420]  [<ffffffff80209e50>] restore_args+0x0/0x30
[  272.539424]  [<ffffffff8023e844>] kthreadd+0xd4/0x160
[  272.539429]  [<ffffffff8023e6f0>] kthread+0x0/0x80
[  272.539433]  [<ffffffff8020a28e>] child_rip+0x0/0x12

Ray
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