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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Jan 2026 14:17:29.4563 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 465ab324-736a-4c92-d636-08de58f7cf8c 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: AMS0EPF000001B6.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR08MB8906 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260121_061739_022401_51D3E309 X-CRM114-Status: GOOD ( 22.22 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Will, > On Mon, Jan 19, 2026 at 10:17:47PM +0000, Yeoreum Yun wrote: > > > > +"2:\n" > > > > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %w0) > > > > + : "+r" (ret), "+Q" (*uaddr), "+r" (*oldval) > > > > + : "r" (newval) > > > > + : "memory"); > > > > > > Don't you need to update *oldval here if the CAS didn't fault? > > > > No. if CAS doesn't make fault the oldval update already. > > Sorry, it was the "+r" constraint with a pointer dereference that threw > me but you have the "memory" clobber so it looks like this will work. > > > > > + > > > > + for (i = 0; i < FUTEX_MAX_LOOPS; i++) { > > > > + if (get_user(oval64.raw, uaddr64)) > > > > + return -EFAULT; > > > > > > Since oldval is passed to us as an argument, can we get away with a > > > 32-bit get_user() here? > > > > It's not a probelm. but is there any sigificant difference? > > I think the code would be clearer if you only read what you actually > use. > > > > > + nval64.raw = oval64.raw; > > > > + > > > > + if (futex_on_lo) { > > > > + oval64.lo_futex.val = oldval; > > > > + nval64.lo_futex.val = newval; > > > > + } else { > > > > + oval64.hi_futex.val = oldval; > > > > + nval64.hi_futex.val = newval; > > > > + } > > > > + > > > > + orig64.raw = oval64.raw; > > > > + > > > > + if (__lsui_cmpxchg64(uaddr64, &oval64.raw, nval64.raw)) > > > > + return -EFAULT; > > > > + > > > > + if (futex_on_lo) { > > > > + oldval = oval64.lo_futex.val; > > > > + other = oval64.lo_futex.other; > > > > + orig_other = orig64.lo_futex.other; > > > > + } else { > > > > + oldval = oval64.hi_futex.val; > > > > + other = oval64.hi_futex.other; > > > > + orig_other = orig64.hi_futex.other; > > > > + } > > > > + > > > > + if (other == orig_other) { > > > > + ret = 0; > > > > + break; > > > > + } > > > > + } > > > > + > > > > + if (!ret) > > > > + *oval = oldval; > > > > > > Shouldn't we set *oval to the value we got back from the CAS? > > > > Since it's a "success" case, the CAS return and oldval must be the same. > > That's why it doesn't matter to use got back from the CAS. > > Otherwise, it returns error and *oval doesn't matter for > > futex_atomic_cmpxchg_inatomic(). > > Got it, but then the caller you have is very weird because e.g. > __lsui_futex_atomic_eor() goes and does another get_user() on the next > iteration instead of using the value returned by the CAS. > > It would probably be clearer if you restructured your CAS helper to look > more like try_cmpxchg() and then the loop around it would be minimal. > You might need to distinguish the faulting case from the comparison > failure case with e.g. -EFAULT vs -EAGAIN. Oh, thanks for pointing this out.I understand your point clearly now. Yes, I’ll respin the patch accordingly. Thanks again! -- Sincerely, Yeoreum Yun