Re: [PATCH v2] ath11k: fix a locking bug in ath11k_mac_op_start()

Dan Carpenter
2021-02-09T08:10:32Z

On Tue, Feb 09, 2021 at 09:47:10AM +0200, Kalle Valo wrote:
> Dan Carpenter <dan.carpenter@oracle.com> writes:
>
> > This error path leads to a Smatch warning:
> >
> > drivers/net/wireless/ath/ath11k/mac.c:4269 ath11k_mac_op_start()
> > error: double unlocked '&ar->conf_mutex' (orig line 4251)
> >
> > We're not holding the lock when we do the "goto err;" so it leads to a
> > double unlock. The fix is to hold the lock for a little longer.
> >
> > Fixes: c83c500b55b6 ("ath11k: enable idle power save mode")
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > v2: reviewers were concern that v1 was racy
> >
> > drivers/net/wireless/ath/ath11k/mac.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/wireless/ath/ath11k/mac.c b/drivers/net/wireless/ath/ath11k/mac.c
> > index c1608f64ea95..464d3425488b 100644
> > --- a/drivers/net/wireless/ath/ath11k/mac.c
> > +++ b/drivers/net/wireless/ath/ath11k/mac.c
> > @@ -4248,8 +4248,6 @@ static int ath11k_mac_op_start(struct ieee80211_hw *hw)
> > /* Configure the hash seed for hash based reo dest ring selection */
> > ath11k_wmi_pdev_lro_cfg(ar, ar->pdev->pdev_id);
> >
> > - mutex_unlock(&ar->conf_mutex);
> > -
> > rcu_assign_pointer(ab->pdevs_active[ar->pdev_idx],
> > &ab->pdevs[ar->pdev_idx]);
> >
> > @@ -4262,6 +4260,9 @@ static int ath11k_mac_op_start(struct ieee80211_hw *hw)
> > goto err;
> > }
> > }
> > +
> > + mutex_unlock(&ar->conf_mutex);
> > +
> > return 0;
> >
> > err:
> > --
> > 2.30.0
>
> But now rcu_assign_pointer() is called while conf_mutex is held,
> previously it was not. I didn't check if this creates problems, but just
> to be on the safe side I modified your patch to keep the original
> functionality. Please check my changes in the pending branch:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&idŽff3667c211072a2107271139b81cbf8c7fd10a
>

I don't think the assignment is a problem, but I'm also fine with the
way you modified the patch. Thanks!

regards,
dan carpenter