Re: [bug report] Maple Tree: add new data structure

[Liam Howlett <liam.howlett@oracle.com>]

* Dan Carpenter <dan.carpenter@oracle.com> [220719 05:36]:
> Hello Liam R. Howlett,
> 
> The patch 058c2f0f755f: "Maple Tree: add new data structure" from Jul
> 17, 2022, leads to the following Smatch static checker warning:
> 
> 	lib/maple_tree.c:6969 mas_validate_limits()
> 	warn: add some parenthesis here? '!piv & (i != 0)'
> 
> lib/maple_tree.c
>     6952 static void mas_validate_limits(struct ma_state *mas)
>     6953 {
>     6954         int i;
>     6955         unsigned long prev_piv = 0;
>     6956         enum maple_type type = mte_node_type(mas->node);
>     6957         void __rcu **slots = ma_slots(mte_to_node(mas->node), type);
>     6958         unsigned long *pivots = ma_pivots(mas_mn(mas), type);
>     6959 
>     6960         /* all limits are fine here. */
>     6961         if (mte_is_root(mas->node))
>     6962                 return;
>     6963 
>     6964         for (i = 0; i < mt_slots[type]; i++) {
>     6965                 unsigned long piv;
>     6966 
>     6967                 piv = mas_safe_pivot(mas, pivots, i, type);
>     6968 
> --> 6969                 if (!piv & (i != 0))
> 
> Sparse and Smatch both hate this.  I think this code is correct and it
> should be:
> 
> 		if ((!piv) & (i != 0))
> 
> However the vast majority of the time this warning indicates a
> precendence bug where what was intended was:
> 
> 	if (!(piv & (i != 0)))

Thanks! I caught this with C=1 (sparse).  I've been working through
another issue with Hugh that was more pressing.  I'll send out a patch
today.  The double && will work here but it shouldn't actually make a
difference.

Regards,
Liam

> 
> 
> I guess it's not common to use booleans for bitwise ANDs...
> 
>     6970                         break;
>     6971 
>     6972                 if (!mte_is_leaf(mas->node)) {
> 
> regards,
> dan carpenter