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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by BN1PEPF0000468B.mail.protection.outlook.com (10.167.243.136) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8445.10 via Frontend Transport; Fri, 14 Feb 2025 04:07:56 +0000 Received: from [10.136.34.113] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Thu, 13 Feb 2025 22:07:53 -0600 Message-ID: Date: Fri, 14 Feb 2025 09:37:50 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched: fix potential use-after-free with cfs bandwidth To: Josh Don , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot CC: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , References: <20250210195117.1074569-1-joshdon@google.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20250210195117.1074569-1-joshdon@google.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Feb 2025 04:07:56.9312 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 55fb8b87-f39b-4da0-579c-08dd4cad29bf X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN1PEPF0000468B.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB6848 Hello Josh, On 2/11/2025 1:21 AM, Josh Don wrote: > We remove the cfs_rq throttled_csd_list entry *before* doing the > unthrottle. The problem with that is that destroy_bandwidth() does a > lockless scan of the system for any non-empty CSD lists. As a result, > it is possible that destroy_bandwidth() returns while we still have a > cfs_rq from the task group about to be unthrottled. > > For full correctness, we should avoid removal from the list until after > we're done unthrottling in __cfsb_csd_unthrottle(). > > For consistency, we make the same change to distribute_cfs_runtime(), > even though this should already be safe due to destroy_bandwidth() > cancelling the bandwidth hrtimers. > > Signed-off-by: Josh Don Other than a small nit: s/destroy_bandwidth/destroy_cfs_bandwidth/g please feel free to add: Reviewed-and-tested-by: K Prateek Nayak -- Thanks and Regards, Prateek > --- > kernel/sched/fair.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 34fe6e9490c2..78f542ab03cf 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5917,10 +5917,10 @@ static void __cfsb_csd_unthrottle(void *arg) > > list_for_each_entry_safe(cursor, tmp, &rq->cfsb_csd_list, > throttled_csd_list) { > - list_del_init(&cursor->throttled_csd_list); > - > if (cfs_rq_throttled(cursor)) > unthrottle_cfs_rq(cursor); > + > + list_del_init(&cursor->throttled_csd_list); > } > > rcu_read_unlock(); > @@ -6034,11 +6034,11 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b) > > rq_lock_irqsave(rq, &rf); > > - list_del_init(&cfs_rq->throttled_csd_list); > - > if (cfs_rq_throttled(cfs_rq)) > unthrottle_cfs_rq(cfs_rq); > > + list_del_init(&cfs_rq->throttled_csd_list); > + > rq_unlock_irqrestore(rq, &rf); > } > SCHED_WARN_ON(!list_empty(&local_unthrottle));