Since commit 6fa2cffe8cf9 ("fakelb: move lock out of iteration"),
fakelb is taking a mutex while holding a spinlock. The patch does
this:
> commit 6fa2cffe8cf937fc10be362a2dcac8a5965f618e
> Author: Alexander Aring <alex.aring@xxxxxxxxx>
> Date: Sun May 17 21:45:04 2015 +0200
>
> fakelb: move lock out of iteration
>
> The list need to be protected while iteration which is need when other
> list iterates at the same time over this list.
>
> Signed-off-by: Alexander Aring <alex.aring@xxxxxxxxx>
> Signed-off-by: Marcel Holtmann <marcel@xxxxxxxxxxxx>
>
> diff --git a/drivers/net/ieee802154/fakelb.c b/drivers/net/ieee802154/fakelb.c
> index c7e7d50..e1c0195 100644
> --- a/drivers/net/ieee802154/fakelb.c
> +++ b/drivers/net/ieee802154/fakelb.c
> @@ -193,9 +193,7 @@ err_reg:
>
> static void fakelb_del(struct fakelb_phy *phy)
> {
> - write_lock_bh(&fakelb_lock);
> list_del(&phy->list);
> - write_unlock_bh(&fakelb_lock);
>
> ieee802154_unregister_hw(phy->hw);
> ieee802154_free_hw(phy->hw);
> @@ -217,8 +215,10 @@ static int fakelb_probe(struct platform_device *pdev)
> return 0;
>
> err_slave:
> + write_lock_bh(&fakelb_lock);
> list_for_each_entry_safe(phy, tmp, &fakelb_phys, list)
> fakelb_del(phy);
> + write_unlock_bh(&fakelb_lock);
> return err;
> }
>
> @@ -226,9 +226,10 @@ static int fakelb_remove(struct platform_device *pdev)
> {
> struct fakelb_phy *phy, *temp;
>
> + write_lock_bh(&fakelb_lock);
> list_for_each_entry_safe(phy, temp, &fakelb_phys, list)
> fakelb_del(phy);
> -
> + write_unlock_bh(&fakelb_lock);
> return 0;
> }
Which causes all of fakelb_del() to run under a spinlock, including
the call to ieee802154_unregister_hw(), which takes a mutex and
flushes a workqueue.
The quick fix is probably to drop the lock for each fakelb_del(phy)
call, i.e. to do something along the lines of:
write_lock_bh(&fakelb_lock);
while (!list_empty(&fakelb_phys)) {
phy = list_first_entry(&fakelb_phys, struct fakelb_phy, list);
write_unlock_bh(&fakelb_lock);
fakelb_del(phy);
write_lock_bh(&fakelb_lock);
}
write_unlock_bh(&fakelb_lock);
I also wonder if the locking here can be converted to RCU or something
like that, as the writer side locking happens very very infrequently.
Any thoughts?
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