Re: [PATCH v2 21/29] nios2: Futex operations

[Ley Foon Tan <lftan@altera.com>]

On Tue, Jul 15, 2014 at 6:03 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Tue, 15 Jul 2014, Ley Foon Tan wrote:
>  +static inline int atomic_futex_op_xchg_set(int oparg, u32 __user *uaddr,
>> +                                        int *oldval)
>> +{
>> +     unsigned long flags;
>> +     int ret;
>> +
>> +     local_irq_save(flags);
>> +
>> +     ret = get_user(*oldval, uaddr);
>> +     if (!ret)
>> +             ret = put_user(oparg, uaddr);
>
> This is wrong as it gets. get_user() might fault and sleep.
>
> You need a proper implementation, which handles fault exceptions.
I have checked that we use nios2 specific get_user() in [1]. This
function will not sleep and it handles fault exception.
I think this should be fine.

[1] http://rocketboards.org/gitweb/?p=linux-socfpga-next.git;a=blob;f=arch/nios2/include/asm/uaccess.h;h=3e36f536afaba24c308a8416a66b8a2573e042a5;hb=refs/heads/nios2-upstream

Regards
Ley Foon