netdev - Re: [PATCH net] ibmvnic: device remove has higher precedence over reset

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Message-ID: <CAOhMmr6LdZQpE7Ah1XVn0ApOO8Ch1XfAuoo1tPNgT0rG0zrc=A@mail.gmail.com>
Date:   Thu, 21 Jan 2021 12:46:23 -0600
From:   Lijun Pan <lijunp213@...il.com>
To:     Dany Madden <drt@...ux.ibm.com>
Cc:     Lijun Pan <ljp@...ux.ibm.com>, netdev@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, sukadev@...ux.ibm.com,
        mpe@...erman.id.au, julietk@...ux.vnet.ibm.com,
        benh@...nel.crashing.org, paulus@...ba.org, davem@...emloft.net,
        Jakub Kicinski <kuba@...nel.org>, gregkh@...uxfoundation.org,
        kernel@...gutronix.de,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH net] ibmvnic: device remove has higher precedence over reset

On Thu, Jan 21, 2021 at 12:42 PM Dany Madden <drt@...ux.ibm.com> wrote:
>
> On 2021-01-20 22:20, Lijun Pan wrote:
> > Returning -EBUSY in ibmvnic_remove() does not actually hold the
> > removal procedure since driver core doesn't care for the return
> > value (see __device_release_driver() in drivers/base/dd.c
> > calling dev->bus->remove()) though vio_bus_remove
> > (in arch/powerpc/platforms/pseries/vio.c) records the
> > return value and passes it on. [1]
> >
> > During the device removal precedure, we should not schedule
> > any new reset (ibmvnic_reset check for REMOVING and exit),
> > and should rely on the flush_work and flush_delayed_work
> > to complete the pending resets, specifically we need to
> > let __ibmvnic_reset() keep running while in REMOVING state since
> > flush_work and flush_delayed_work shall call __ibmvnic_reset finally.
> > So we skip the checking for REMOVING in __ibmvnic_reset.
> >
> > [1]
> > https://lore.kernel.org/linuxppc-dev/20210117101242.dpwayq6wdgfdzirl@pengutronix.de/T/#m48f5befd96bc9842ece2a3ad14f4c27747206a53
> > Reported-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > Fixes: 7d7195a026ba ("ibmvnic: Do not process device remove during
> > device reset")
> > Signed-off-by: Lijun Pan <ljp@...ux.ibm.com>
> > ---
> > v1 versus RFC:
> >   1/ articulate why remove the REMOVING checking in __ibmvnic_reset
> >   and why keep the current checking for REMOVING in ibmvnic_reset.
> >   2/ The locking issue mentioned by Uwe are being addressed separately
> >      by       https://lists.openwall.net/netdev/2021/01/08/89
> >   3/ This patch does not have merge conflict with 2/
> >
> >  drivers/net/ethernet/ibm/ibmvnic.c | 8 +-------
> >  1 file changed, 1 insertion(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/ibm/ibmvnic.c
> > b/drivers/net/ethernet/ibm/ibmvnic.c
> > index aed985e08e8a..11f28fd03057 100644
> > --- a/drivers/net/ethernet/ibm/ibmvnic.c
> > +++ b/drivers/net/ethernet/ibm/ibmvnic.c
> > @@ -2235,8 +2235,7 @@ static void __ibmvnic_reset(struct work_struct
> > *work)
> >       while (rwi) {
> >               spin_lock_irqsave(&adapter->state_lock, flags);
> >
> > -             if (adapter->state == VNIC_REMOVING ||
> > -                 adapter->state == VNIC_REMOVED) {
> > +             if (adapter->state == VNIC_REMOVED) {
>
> If we do get here, we would crash because ibmvnic_remove() happened. It
> frees the adapter struct already.

Not exactly. viodev is gone; netdev is done; ibmvnic_adapter is still there.

Lijun
>
> >                       spin_unlock_irqrestore(&adapter->state_lock, flags);
> >                       kfree(rwi);
> >                       rc = EBUSY;
> > @@ -5372,11 +5371,6 @@ static int ibmvnic_remove(struct vio_dev *dev)
> >       unsigned long flags;
> >
> >       spin_lock_irqsave(&adapter->state_lock, flags);
> > -     if (test_bit(0, &adapter->resetting)) {
> > -             spin_unlock_irqrestore(&adapter->state_lock, flags);
> > -             return -EBUSY;
> > -     }
> > -
> >       adapter->state = VNIC_REMOVING;
> >       spin_unlock_irqrestore(&adapter->state_lock, flags);