On Wed, Jun 11, 2025 at 05:36:51PM +0000, Long Li wrote:
> > Subject: Re: [PATCH net-next 1/4] net: mana: Fix potential deadlocks in mana
> > napi ops
> >
> > On Wed, Jun 11, 2025 at 04:03:52AM -0700, Saurabh Singh Sengar wrote:
> > > On Wed, Jun 11, 2025 at 01:46:13AM -0700, Erni Sri Satya Vennela wrote:
> > > > When net_shaper_ops are enabled for MANA, netdev_ops_lock becomes
> > > > active.
> > > >
> > > > The netvsc sets up MANA VF via following call chain:
> > > >
> > > > netvsc_vf_setup()
> > > > dev_change_flags()
> > > > ...
> > > > __dev_open() OR __dev_close()
> > > >
> > > > dev_change_flags() holds the netdev mutex via netdev_lock_ops.
> > > >
> > > > During this process, mana_create_txq() and mana_create_rxq() invoke
> > > > netif_napi_add_tx(), netif_napi_add_weight(), and napi_enable(), all
> > > > of which attempt to acquire the same lock, leading to a potential
> > > > deadlock.
> > >
> > > commit message could be better oriented.
> > >
> > > >
> > > > Similarly, mana_destroy_txq() and mana_destroy_rxq() call
> > > > netif_napi_disable() and netif_napi_del(), which also contend for
> > > > the same lock.
> > > >
> > > > Switch to the _locked variants of these APIs to avoid deadlocks when
> > > > the netdev_ops_lock is held.
> > > >
> > > > Fixes: d4c22ec680c8 ("net: hold netdev instance lock during
> > > > ndo_open/ndo_stop")
> > > > Signed-off-by: Erni Sri Satya Vennela <er...@linux.microsoft.com>
> > > > Reviewed-by: Haiyang Zhang <haiya...@microsoft.com>
> > > > Reviewed-by: Shradha Gupta <shradhagu...@linux.microsoft.com>
> > > > ---
> > > > drivers/net/ethernet/microsoft/mana/mana_en.c | 39
> > > > ++++++++++++++-----
> > > > 1 file changed, 30 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > > b/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > > index ccd2885c939e..3c879d8a39e3 100644
> > > > --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > > +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > > @@ -1911,8 +1911,13 @@ static void mana_destroy_txq(struct
> > mana_port_context *apc)
> > > > napi = &apc->tx_qp[i].tx_cq.napi;
> > > > if (apc->tx_qp[i].txq.napi_initialized) {
> > > > napi_synchronize(napi);
> > > > - napi_disable(napi);
> > > > - netif_napi_del(napi);
> > > > + if (netdev_need_ops_lock(napi->dev)) {
> > > > + napi_disable_locked(napi);
> > > > + netif_napi_del_locked(napi);
> > > > + } else {
> > > > + napi_disable(napi);
> > > > + netif_napi_del(napi);
> > > > + }
> > >
> > > Instead of using if-else, we can used netdev_lock_ops(), followed by
> > > *_locked
> > api-s.
> > > Same for rest of the patch.
> > >
> >
> > I later realized that what we actually need is:
> >
> > if (!netdev_need_ops_lock(napi->dev))
> > netdev_lock(dev);
> >
> > not
> >
> > if (netdev_need_ops_lock(napi->dev))
> > netdev_lock(dev);
> >
> > Hence, netdev_lock_ops() is not appropriate. Instead,
> > netdev_lock_ops_to_full()
> > seems to be a better choice.
>
> Yes, netdev_lock_ops_to_full() seems better
Thankyou, Saurabh and Long, for the suggestion. I'll make sure to
incorporate this API in my next version.
> Long
