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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Sep 2025 22:34:57.5696 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 04068858-b714-44d4-b18f-08ddf4a8198a X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DU2PEPF00028D06.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM9PR08MB6657 Hi Catalin, > > > On Sat, Aug 16, 2025 at 04:19:27PM +0100, Yeoreum Yun wrote: > > > > diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h > > > > index bc06691d2062..ab7003cb4724 100644 > > > > --- a/arch/arm64/include/asm/futex.h > > > > +++ b/arch/arm64/include/asm/futex.h > > > > @@ -7,17 +7,21 @@ > > > > > > > > #include > > > > #include > > > > +#include > > > > > > > > #include > > > > > > > > -#define FUTEX_MAX_LOOPS 128 /* What's the largest number you can think of? */ > > > > +#define LLSC_MAX_LOOPS 128 /* What's the largest number you can think of? */ > > > > > > I just noticed - you might as well leave the name as is here, especially > > > if in patch 6 you align down address and use CAS on a 64-bit value as > > > per Will's comment (and it's no longer LLSC). I think renaming this is > > > unnecessary. > > > > Okay. I'll restore to use origin name. > > But I think LSUI wouldn't be used with CAS according to patch 6's > > comments from you and additionally i think > > chaning the CAS would make a failure because of > > change of unrelated field. i.e) > > > > struct user_structure{ > > uint32 futex; > > uint32 some_value; > > }; > > > > In this case, the change of some_value from user side could make a > > failure of futex atomic operation. > > Yes but the loop would read 'some_value' again, fold in 'futex' and > retry. It would eventually succeed or fail after 128 iterations if the > user keeps changing that location. Note that's also the case with LL/SC, > the exclusive monitor would be cleared by some store in the same cache > line (well, depending on the hardware implementation) and the STXR fail. > From this perspective, CAS has better chance of succeeding. Oh. I see Thanks for insight ;) > > > So I think it would be better to keep the current LLSC implementation > > in LSUI. > > I think the code would look simpler with LL/SC but you can give it a try > and post the code sample here (not in a new series). Okay. I'll try. > > BTW, is there a test suite for all the futex operations? The cover > letter did not mention any. with selftest's futex testcase, I've tested. But Since there is no test for each operation even in LTP, I tested it with additional test from me. > > -- > Catalin -- Sincerely, Yeoreum Yun