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Mon, 25 Nov 2024 10:16:16 GMT Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2D77B5805C; Mon, 25 Nov 2024 10:16:16 +0000 (GMT) Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id F3A4058051; Mon, 25 Nov 2024 10:16:08 +0000 (GMT) Received: from [9.43.78.113] (unknown [9.43.78.113]) by smtpav02.dal12v.mail.ibm.com (Postfix) with ESMTP; Mon, 25 Nov 2024 10:16:08 +0000 (GMT) Message-ID: <70dfefef-aaa3-43be-9f8a-85adc07942fc@linux.ibm.com> Date: Mon, 25 Nov 2024 15:46:06 +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 1/2] sched/fair: Fix panic if NEXT_BUDDY enabled Content-Language: en-US To: Adam Li , peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org Cc: dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org, patches@amperecomputing.com, cl@linux.com, Madadi Vineeth Reddy References: <20241125021222.356881-1-adamli@os.amperecomputing.com> <20241125021222.356881-2-adamli@os.amperecomputing.com> Reply-To: 20241125021222.356881-2-adamli@os.amperecomputing.com From: Madadi Vineeth Reddy In-Reply-To: <20241125021222.356881-2-adamli@os.amperecomputing.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: BUA2UfnhMiMA5ls-7Mxg8636LPz0lXRA X-Proofpoint-ORIG-GUID: TDVFoqJgC9nnFzPEaUIydKAR76TG_DTG X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-15_01,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 mlxscore=0 suspectscore=0 phishscore=0 mlxlogscore=846 spamscore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 impostorscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2411250085 On 25/11/24 07:42, Adam Li wrote: > Enabling NEXT_BUDDY may trigger warning and kernel panic: > > [ 124.977300] cfs_rq->next->sched_delayed > [ 124.977310] WARNING: CPU: 51 PID: 2150 at kernel/sched/fair.c:5621 pick_task_fair+0x130/0x150 > > [ 297.371198] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000051 > [ 297.406112] CPU: 116 UID: 0 PID: 10328 Comm: Grizzly-worker( Tainted: G W E 6.12.0.adam+ #1 > [ 297.597362] Call trace: > [ 297.599795] pick_task_fair+0x50/0x150 (P) > [ 297.603879] pick_task_fair+0x50/0x150 (L) > [ 297.607963] pick_next_task_fair+0x30/0x3c0 > [ 297.612134] __pick_next_task+0x4c/0x220 > [ 297.616045] pick_next_task+0x44/0x980 > [ 297.619782] __schedule+0x3d0/0x628 > [ 297.623259] do_task_dead+0x50/0x60 > [ 297.626736] do_exit+0x28c/0x410 > [ 297.629955] do_group_exit+0x3c/0xa0 > [ 297.633518] get_signal+0x8c4/0x8d0 > [ 297.636996] do_signal+0x9c/0x270 > [ 297.640299] do_notify_resume+0xe0/0x198 > [ 297.644212] el0_svc+0xf4/0x170 > [ 297.647342] el0t_64_sync_handler+0x10c/0x138 > [ 297.651687] el0t_64_sync+0x1ac/0x1b0 > [ 297.655339] Code: d503201f 1400002a aa1403e0 97ffda0b (39414401) > [ 297.661439] ---[ end trace 0000000000000000 ]--- > [ 297.726593] Kernel panic - not syncing: Oops: Fatal exception > > Do not set next buddy if sched_delayed is set. > > Signed-off-by: Adam Li > --- > kernel/sched/fair.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index fbdca89c677f..cd1188b7f3df 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8748,6 +8748,8 @@ static void set_next_buddy(struct sched_entity *se) > return; > if (se_is_idle(se)) > return; > + if (se->sched_delayed) > + return; IIUC, this happens due to a race condition between choosing the next_buddy and dequeuing the task from the runqueue as soon as its lag becomes zero, thereby causing task_of(se) to result in a null dereference in pick_task_fair? Correct me if I am wrong. Thanks, Madadi Vineeth Reddy > cfs_rq_of(se)->next = se; > } > }