On Tue, Mar 31, 2020 at 09:40:37AM +0800, Boqun Feng wrote: > On Fri, Mar 27, 2020 at 06:18:43PM -0400, Joel Fernandes wrote: > > On Thu, Mar 26, 2020 at 10:40:18AM +0800, Boqun Feng wrote: > > > A recent discussion raises up the requirement for having test cases for > > > atomic APIs: > > > > > > https://lore.kernel.org/lkml/20200213085849.GL14897@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > > > > , and since we already have a way to generate a test module from a > > > litmus test with klitmus[1]. It makes sense that we add more litmus > > > tests for atomic APIs. And based on the previous discussion, I create a > > > new directory Documentation/atomic-tests and put these litmus tests > > > here. > > > > > > This patchset starts the work by adding the litmus tests which are > > > already used in atomic_t.txt, and also improve the atomic_t.txt to make > > > it consistent with the litmus tests. > > > > > > Previous version: > > > v1: https://lore.kernel.org/linux-doc/20200214040132.91934-1-boqun.feng@xxxxxxxxx/ > > > v2: https://lore.kernel.org/lkml/20200219062627.104736-1-boqun.feng@xxxxxxxxx/ > > > v3: https://lore.kernel.org/linux-doc/20200227004049.6853-1-boqun.feng@xxxxxxxxx/ > > > > For full series: > > > > Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > > > One question I had was in the existing atomic_set() documentation, it talks > > about atomic_add_unless() implementation based on locking could have issues. > > It says the way to fix such cases is: > > > > Quote: > > the typical solution is to then implement atomic_set{}() with > > atomic_xchg(). > > > > I didn't get how using atomic_xchg() fixes it. Is the assumption there that > > atomic_xchg() would be implemented using locking to avoid atomic_set() having > > Right, I think that's the intent of the sentence. > > > issues? If so, we could clarify that in the document. > > > > Patches are welcome ;-) ---8<----------------------- Like this? I'll add it to my tree and send it to Paul during my next series, unless you disagree ;-) Subject: [PATCH] doc: atomic_t: Document better about the locking within atomic_xchg() It is not fully clear how the atomic_set() would not cause an issue with preservation of the atomicity of RMW in this example. Make it clear that locking within atomic_xchg() would save the day. Suggested-by: Boqun Feng <boqun.feng@xxxxxxxxx> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> --- Documentation/atomic_t.txt | 2 ++ 1 file changed, 2 insertions(+) diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt index 0f1fdedf36bbb..1d9c307c73a7c 100644 --- a/Documentation/atomic_t.txt +++ b/Documentation/atomic_t.txt @@ -129,6 +129,8 @@ with a lock: unlock(); the typical solution is to then implement atomic_set{}() with atomic_xchg(). +The locking within the atomic_xchg() in CPU1 would ensure that the value read +in CPU0 would not be overwritten. RMW ops: -- 2.26.0.292.g33ef6b2f38-goog
