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Mon, 9 Nov 2026 14:02:14 +0000 (GMT) Received: from [9.124.212.131] (unknown [9.124.212.131]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 9 Nov 2026 14:02:14 +0000 (GMT) Message-ID: <3dcbccdd-0a50-4b57-b0bf-79b55911bfa2@linux.ibm.com> Date: Mon, 9 Nov 2026 19:32:13 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched/core: Fix a TOCTOU bug in sched_non_preferred_cpu_push_stop() To: Fushuai Wang , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com Cc: linux-kernel@vger.kernel.org, wangfushuai@baidu.com References: <20261109083130.1679-1-fushuai.wang@linux.dev> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20261109083130.1679-1-fushuai.wang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: zYsDelZRSbXhCTEZOMhRxQxOVhhSe8YN X-Authority-Analysis: v=2.4 cv=PeVqFShd c=1 sm=1 tr=0 ts=6af1d26c cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=zuLzuavZAAAA:8 a=Tcm3tUNZ0R_kjyZ4jMMA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: 1e8m9KwYVgcXC1Q7GQJQa0W6oYz8uTud X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTA5MDA1NCBTYWx0ZWRfX8b4U1fmmF+AP GFryA8IJEwGmWVed1rM/d/L8nA83w7XVkz6NBvMLodrxkrWoTdISe4+iPDvH7xH3a8OFg8j+0tS FE8gFjRhb1FauJeb6fJxLgu3xpW8MWvVDZA3AJXbidMD9whvV+Tx3cj/7xcKS9jVxg6iQ0Ei3xE 2ISZ7APCnCS/+gdlhOIq8i1xDSo5BBSjxkh8y34TvDwsxZyCB6gFqu4gkgTInMiT6LrSlE9bNrk x3nG4uUZkU6HwyaHs1iso/6mOKn6oNyHWqSa3eVMPpmVZeHrtJg9DKJe3hclSE4dRsjvWS6zP+h A08DybKiBBN/zmClLegQcwPS1WT9xxvIbdVrinBtGsTvaajWMbaTgWoCP5rctdPTpnyEC9o4YqL oDrfZ/S//y4TluvkXlA3ZhNx4qMMKHc+IMy3IKvZMtvasnIY9oCCppgxUzPOtMvMnmkZINgPIQW nOzWWTiM02sTIcuUOxQ== X-Proofpoint-Spam-Info: AW1haW4tMjYxMTA5MDA1NCBTYWx0ZWRfX2Mk90JOwu154 vc9G3wrXUvTz6tuXWOSJ1I8VqVEMxefCq6jlAYCsWFXRe5wHErBggFWLZIRnJq4ANh72bmU7IK7 W9p0fbLkxfmIyb4Sn/v51eR2a2ZD0h4= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-09_05,2026-11-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 phishscore=0 suspectscore=0 impostorscore=0 priorityscore=1501 lowpriorityscore=0 spamscore=0 malwarescore=0 clxscore=1011 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2611040001 definitions=main-2611090054 Hi Fushuai. On 11/9/26 2:01 PM, Fushuai Wang wrote: > From: Fushuai Wang > > sched_push_current_non_preferred_cpu() is called in irq context. It > checks is_migration_disabled() before queuing the stopper, but the > task may continue running and enter migrate_disable() before the stopper > runs. > Recheck is_migration_disabled() in sched_non_preferred_cpu_push_stop() > before calling __migrate_task(). > > WARNING: kernel/sched/core.c:3432 at set_task_cpu+0x1b8/0xdf0, CPU#21: migration/21/152 > Stopper: sched_non_preferred_cpu_push_stop+0x0/0xb10 <- sched_push_current_non_preferred_cpu+0x6a6/0x9a0 > ... > Call Trace: > > ? __this_cpu_preempt_check+0x13/0x20 > move_queued_task+0xfc/0x650 > ? is_cpu_allowed+0x341/0x820 > ? __this_cpu_preempt_check+0x13/0x20 > sched_non_preferred_cpu_push_stop+0x7b7/0xb10 > ? __pfx_sched_non_preferred_cpu_push_stop+0x10/0x10 > ... > > How does rest of the stack look like? Is it disabling preemption where stopper is not getting a chance to run before task sets migrate_disable? > Fixes: 74699f56ebcf ("sched/core: Push current task from non preferred CPU") > Signed-off-by: Fushuai Wang > --- > kernel/sched/core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 1a088d4576f5..8ed7613eafd6 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -11317,7 +11317,8 @@ static int sched_non_preferred_cpu_push_stop(void *arg) > rq->npc_push_work_pending = false; > update_rq_clock(rq); > > - if (task_rq(p) == rq && task_on_rq_queued(p)) { > + if (task_rq(p) == rq && task_on_rq_queued(p) && > + !is_migration_disabled(p)) { > struct rq *dest_rq = __migrate_task(rq, &rf, p, cpu); > I thought it is unnecessary. https://lore.kernel.org/all/4e2421fe-4b26-4d92-8709-bfa8d3a4114a@linux.ibm.com/#t Can you share how you are running into this? > if (rq != dest_rq)