netdev - Re: [PATCH] netconsole: release the spinlock before __netpoll

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Date:	Mon, 11 Mar 2013 07:30:24 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Veaceslav Falico <darkmag@...il.com>
Cc:	Veaceslav Falico <vfalico@...hat.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	amwang@...hat.com
Subject: Re: [PATCH] netconsole: release the spinlock before
 __netpoll_cleanup()

On Mon, Mar 11, 2013 at 11:08:02AM +0100, Veaceslav Falico wrote:
> On Sun, Mar 10, 2013 at 4:25 PM, Veaceslav Falico <vfalico@...hat.com> wrote:
> > On Thu, Mar 07, 2013 at 04:14:38PM -0500, David Miller wrote:
> >>
> ...snip...
> >> Quite a bit of email corruption of this patch.
> >
> >
> > Sorry, somehow messed it.
> >
> >
> >>
> >> Also, this code block is probably too deeply indented to be sane,
> >> consider creating a small helper function to call instead.
> >
> >
> > It gets quite ugly if I try to move it to another function. However, maybe
> > something like that will work - it's effectively the same code, just that
> > I've moved the long part out of the if () { } block. Looks a lot more
> > readable, though one line still breaks 80chars limit. I've reworked the
> > subject/commit message too.
> >
> > Subject: [PATCH] netconsole: don't call __netpoll_cleanup() while atomic
> >
> > __netpoll_cleanup() is called in netconsole_netdev_event() while holding a
> > spinlock. Release/acquire the spinlock before/after it and restart the
> >
> > loop.
> >
> > Signed-off-by: Veaceslav Falico <vfalico@...hat.com>
> > ---
> >    drivers/net/netconsole.c |   22 +++++++++++++++-------
> >    1 files changed, 15 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> > index 37add21..38eaa8c 100644
> >
> > --- a/drivers/net/netconsole.c
> > +++ b/drivers/net/netconsole.c
> > @@ -666,6 +666,7 @@ static int netconsole_netdev_event(struct notifier_block
> > *this,
> >                 goto done;
> >         spin_lock_irqsave(&target_list_lock, flags);
> > +restart:
> >         list_for_each_entry(nt, &target_list, list) {
> >                 netconsole_target_get(nt);
> >                 if (nt->np.dev == dev) {
> > @@ -679,14 +680,21 @@ static int netconsole_netdev_event(struct
> > notifier_block *this,
> >                                 /*
> >
> >                                  * rtnl_lock already held
> >                                  */
> > -                               if (nt->np.dev) {
> > -                                       __netpoll_cleanup(&nt->np);
> > -                                       dev_put(nt->np.dev);
> > -                                       nt->np.dev = NULL;
> > +                               if (!nt->np.dev) {
> > +                                       nt->enabled = 0;
> > +                                       stopped = true;
> > +                                       break;
> >                                 }
> > -                               nt->enabled = 0;
> > -                               stopped = true;
> > -                               break;
> > +                               /*
> > +                                * we might sleep in __netpoll_cleanup()
> > +                                */
> > +                               spin_unlock_irqrestore(&target_list_lock,
> > flags);
> > +                               __netpoll_cleanup(&nt->np);
> > +                               spin_lock_irqsave(&target_list_lock, flags);
> > +                               dev_put(nt->np.dev);
> > +                               nt->np.dev = NULL;
> >
> > +                               netconsole_target_put(nt);
> > +                               goto restart;
> >                         }
> >                 }
> >                 netconsole_target_put(nt);
> > --
> > 1.7.1
> 
> Self-NAK this patch, I've triggered another kernel panic with it. Will
> send another one shortly. Basicly, the whole if (!nt->np.dev) is not
> needed and nt->enabled=0 should always be set, otherwise we
> end up with nt->np.dev == NULL and nt->enabled == 1, thus
> triggering panics in places like write_msg(), where it verifies only
> if the nt->enabled is true.
> 
Yup, I think you want to make the nt->enabled and stopped statements
unconditional, and precedede the whole block with a if(!nt->np.dev) { continue;}
statement.
Neil

> -- 
> Best regards,
> Veaceslav Falico
> 
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