Hi Arnd,
Thank you for your feedback.
Às 05:50 de 17/08/21, Arnd Bergmann escreveu:
> On Fri, Jul 9, 2021 at 2:13 AM André Almeida <andrealmeid@xxxxxxxxxxxxx> wrote:
>>
>> Add support to wait on multiple futexes. This is the interface
>> implemented by this syscall:
>>
>> futex_waitv(struct futex_waitv *waiters, unsigned int nr_futexes,
>> unsigned int flags, struct timespec *timo)
>>
>> struct futex_waitv {
>> __u64 val;
>> void *uaddr;
>> unsigned int flags;
>> };
>
> You should generally try to avoid structures with implicit padding
> like this one.
>
>> arch/x86/entry/syscalls/syscall_32.tbl | 1 +
>> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
>> include/linux/compat.h | 9 +
>> include/linux/futex.h | 108 ++++++--
>> include/uapi/asm-generic/unistd.h | 4 +-
>
> I would split out the syscall table changes from the implementation, but then
> do the table changes for all architectures, at least when you get to a version
> that gets close to being accepted.
>
Ok, I'll make sure to do that.
>> +#ifdef CONFIG_COMPAT
>> +/**
>> + * compat_futex_parse_waitv - Parse a waitv array from userspace
>> + * @futexv: Kernel side list of waiters to be filled
>> + * @uwaitv: Userspace list to be parsed
>> + * @nr_futexes: Length of futexv
>> + *
>> + * Return: Error code on failure, pointer to a prepared futexv otherwise
>> + */
>> +static int compat_futex_parse_waitv(struct futex_vector *futexv,
>> + struct compat_futex_waitv __user *uwaitv,
>> + unsigned int nr_futexes)
>> +{
>> + struct compat_futex_waitv aux;
>> + unsigned int i;
>> +
>> + for (i = 0; i < nr_futexes; i++) {
>> + if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
>> + return -EFAULT;
>> +
>> + if ((aux.flags & ~FUTEXV_WAITER_MASK) ||
>> + (aux.flags & FUTEX_SIZE_MASK) != FUTEX_32)
>> + return -EINVAL;
>> +
>> + futexv[i].w.flags = aux.flags;
>> + futexv[i].w.val = aux.val;
>> + futexv[i].w.uaddr = compat_ptr(aux.uaddr);
>> + futexv[i].q = futex_q_init;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +COMPAT_SYSCALL_DEFINE4(futex_waitv, struct compat_futex_waitv __user *, waiters,
>> + unsigned int, nr_futexes, unsigned int, flags,
>> + struct __kernel_timespec __user *, timo)
>> +{
>> + struct hrtimer_sleeper to;
>> + struct futex_vector *futexv;
>> + struct timespec64 ts;
>> + ktime_t time;
>> + int ret;
>
> It would be nice to reduce the duplication a little. compat_sys_futex_waitv()
> and sys_futex_waitv() only differ by a single line, in which they call
> a different
> parse function, and the two parse functions only differ in the layout of the
> user space structure. The get_timespec64() call already has an
> in_compat_syscall() check in it, so I would suggest having a single entry
> point for native and compat mode, but either having the parse function
> add another such check or making the structure layout compatible.
>
> The normal way of doing this is to have a __u64 value instead of the pointer,
> and then using u64_to_uptr() for the conversion. It might be nice to
> add a global
>
> typedef __u64 __kernel_uptr_t;
>
> for this purpose.
>
You're right, I could save a lot of lines doing that. I wasn't aware
that get_timespec64() was "compat-aware". I'll apply those changes for
my next version.
> Arnd
>
