Hi Arnd,
Em 24/10/2024 12:57, Arnd Bergmann escreveu:
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.
Ok
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?
Oh right, I haven't covered that indeed. I think I would need to have
something like:
static void exit_robust_list_64()
static void exit_robust_list_32()
And then each function would use explicit sizes for pointers. Also, I
would rewrite the conditions to make that every combination of 64/32bit
kernel/app calls the appropriated function.
Alternatively, we could just disable 32bit kernel/app to use the
ROBUST_LIST_64BIT option.
Thank you for your feedback!
André
