Hi David,
On Sat, 07 Dec 2024 08:04:56 +0000, David Howells wrote:
> Akira Yokosawa <akiyks@xxxxxxxxx> wrote:
>
>> Are you sure removing the smp_rmb() is realy the right thing to do?
>
> The wait_on_bit*() class functions, e.g.:
>
> wait_on_bit(unsigned long *word, int bit, unsigned mode)
> {
> might_sleep();
> if (!test_bit_acquire(bit, word))
> return 0;
> return out_of_line_wait_on_bit(word, bit,
> bit_wait,
> mode);
> }
>
> now unconditionally includes an appropriate barrier on the test_bit(), so the
> smp_rmb() should be unnecessary, though netfslib should probably be using
> clear_and_wake_up_bit().
>
Thank you for clarifying.
> Probably we need to update the doc to reflect this.
Agreed.
I see that wait_on_bit()'s kernel-doc comment mentions implicit ACQUIRE
semantics on success, and that of wake_up_bit() mentions the need of care
for memory ordering before calling it.
Unfortunately, neither of those comments is included into kernel
documentation build (Sphinx) at the moment.
I'm going to prepare a patch for including them somewhere under the
core-api doc.
WRT memory-barriers.txt, I'm not sure I can update it properly.
David, may I ask you doing that part?
Thanks, Akira
