On Wed, 6 Mar 2024 at 18:43, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I dunno.
Oh, and just looking at that patch, I still think the code is confused.
On the reading side, we have:
pipe_count = smp_load_acquire(&p->rtort_pipe_count);
if (pipe_count > RCU_TORTURE_PIPE_LEN) {
/* Should not happen, but... */
where that comment clearly says that the pipe_count we read (whether
with READ_ONCE() or with my smp_load_acquire() suggestion) should
never be larger than RCU_TORTURE_PIPE_LEN.
But the writing side very clearly did:
i = rp->rtort_pipe_count;
if (i > RCU_TORTURE_PIPE_LEN)
i = RCU_TORTURE_PIPE_LEN;
...
smp_store_release(&rp->rtort_pipe_count, ++i);
(again, syntactically it could have been "i + 1" instead of my "++i" -
same value), so clearly the writing side *can* write a value that is >
RCU_TORTURE_PIPE_LEN.
So while the whole READ/WRITE_ONCE vs smp_load_acquire/store_release
is one thing that might be worth looking at, I think there are other
very confusing aspects here.
Linus
