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b=mT5oxnWZ0w5/+cdNOlzRJmq7nRHblfGogfixAFNcmsQcFzBy/8eYn4yLawm316RnPJeSDgOSbPKiIlgdkMG0Pi1D26gQ5wGCKyAk9oB231fCPyoA0UYPphjNNNPvhYcaD/R+pdrxJcwNb+jJ4RP5sOuQQWTn6wiOF7GGDtXDLzY= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from SN7PR12MB8148.namprd12.prod.outlook.com (2603:10b6:806:351::17) by PH7PR12MB9224.namprd12.prod.outlook.com (2603:10b6:510:2e7::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.71.13; Thu, 28 May 2026 19:04:56 +0000 Received: from SN7PR12MB8148.namprd12.prod.outlook.com ([fe80::8262:5400:b63d:c8a2]) by SN7PR12MB8148.namprd12.prod.outlook.com ([fe80::8262:5400:b63d:c8a2%6]) with mapi id 15.21.0071.011; Thu, 28 May 2026 19:04:56 +0000 Message-ID: <6a0a2f88-c22f-4a08-b3cd-b46e9677caba@amd.com> Date: Thu, 28 May 2026 14:04:53 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 8/9] x86/resctrl: Ensure domain fully initialized before placed on RCU list To: Reinette Chatre , tony.luck@intel.com, james.morse@arm.com, Dave.Martin@arm.com, bp@alien8.de, tglx@linutronix.de, dave.hansen@linux.intel.com Cc: x86@kernel.org, hpa@zytor.com, ben.horgan@arm.com, fustini@kernel.org, fenghuay@nvidia.com, peternewman@google.com, yu.c.chen@intel.com, linux-kernel@vger.kernel.org, patches@lists.linux.dev References: <3ba2959b1cd3596e1e340eaee6b43487edaec0a4.1779476724.git.reinette.chatre@intel.com> <4053bd27-bca3-4745-9f34-65843e250f12@intel.com> Content-Language: en-US From: Babu Moger In-Reply-To: <4053bd27-bca3-4745-9f34-65843e250f12@intel.com> Content-Type: text/plain; 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>> } >> >> - list_add_tail_rcu(&d->hdr.list, add_pos); >> - >> err = resctrl_online_mon_domain(r, &d->hdr); >> if (err) { >> - list_del_rcu(&d->hdr.list); >> - synchronize_rcu(); >> l3_mon_domain_free(hw_dom); >> + return; >> } >> + list_add_tail_rcu(&d->hdr.list, add_pos); >> } >> >> static void domain_add_cpu_mon(int cpu, struct rdt_resource *r) > > I resubmitted the last three patches of series to obtain Sashiko review [1] and > respond to that feedback here: > > a) Sashiko: "Does this reordering expose the monitor directories to userspace before the > domain is actually added to the RCU list?" > > Yes. As pointed out by Sashiko there is a short time where the monitoring data files > may be exposed to user space before the monitoring domain is added to the RCU list. > Also pointed out by Sashiko, if user attempts to read from such file it will return > -ENOENT. > > This behavior looks correct and acceptable to me. Yes. I agree, > > b) Sashiko: "This is a pre-existing issue, but does resctrl_find_domain() safely traverse > the RCU list? > Yes, this is safe because resctrl_find_domain() is run with cpus_read_lock() that ensures > the list can be traversed safely because the list can only be modified with > CPU write lock held. > One improvement to resctrl that would help support this is to replace the "list_for_each()" > domain list traversals with something like: > list_for_each_entry_rcu(pos, head, member, lockdep_is_cpus_held()) > Doing something like above would help document why such list traversal outside of > RCU read-side critical section is safe. Are you planning to make this change at this time? It appears to be a corner case, and we haven’t observed it in real-world scenarios. Thanks Babu