linux-kernel - Re: [PATCH] make hci_notifier a blocking notifier (was Re: BUG: sleeping function called from invalid context at net/core/sock.c:1523)

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Message-ID: <a781481a0705061656u37b90022jfded9b1edbea3fa5@mail.gmail.com>
Date:	Mon, 7 May 2007 05:26:05 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Ray Lee" <ray-lk@...rabbit.org>
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)

(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.

Thanks,
Satyam
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