On Thu, Oct 24, 2024, at 14:57, André Almeida wrote:
> This new syscall allows to set multiple list to the same process. There
> are two list types: 32 and 64 bit lists.
>
> It supports up to 10 lists per process (see ROBUST_LISTS_PER_TASK). The
> lists are dynamically allocated on demand, as part of a linked list.
> This is the proposed interface:
>
> long set_robust_list2(void *head, int index, unsigned int flags)
>
> Userspace can ask to set the head of a new list using (index = -1).
> Kernel will allocate a new list, place in the linked list and return the
> new index to userspace.
>
> Userspace can modify an existing head by using an index >= 0. If the
> requested list doesn't exist, an error is returned.
>
> Userspace cannot remove a robust list.
>
> For now, flag is for the list type:
>
> enum robust_list_type {
> ROBUST_LIST_32BIT,
> ROBUST_LIST_64BIT,
> };
>
> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
Hi André,
I have no opinion on the syscall itself, but I'll comment on
the way you hook it up:
> arch/arm/tools/syscall.tbl | 1 +
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
If we agree on the number, this should be added to all
architectures at the same time. In particular, when
you add it to 32-bit arm, it also needs to be in the
corresponding arch/arm64/tools/syscall_32.tbl for
compat mode.
> include/uapi/asm-generic/unistd.h | 5 +-
This reminds me that I need to send the patch to remove this
file, nothing should use it any more, though we still have
the copy in tools/include/uapi/asm-generic/unistd.h that
still gets referenced until the scripts are changed to
use the syscall.tbl format.
> + if (unlikely(!list_empty(list2))) {
> + list_for_each_entry_safe(curr, n, list2, list) {
> + if (curr->head != NULL) {
> + if (curr->list_type == ROBUST_LIST_64BIT)
> + exit_robust_list(tsk, curr->head);
> + else if (curr->list_type == ROBUST_LIST_32BIT)
> + compat_exit_robust_list(tsk, curr->head);
> + curr->head = NULL;
> + }
This looks like the behavior of a 32-bit task using
ROBUST_LIST_64BIT is different on native 32-bit kernels
compared to running on compat mode.
Assuming we want them to behave the same way, did you intend
ROBUST_LIST_64BIT to refer to 64-bit pointers on 32-bit
tasks, or should they use normal word-size pointers?
Arnd
