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Wed, 19 Nov 2025 16:54:32 GMT Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4750658065; Wed, 19 Nov 2025 16:54:32 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E573F58069; Wed, 19 Nov 2025 16:54:26 +0000 (GMT) Received: from [9.61.247.101] (unknown [9.61.247.101]) by smtpav05.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 19 Nov 2025 16:54:26 +0000 (GMT) Message-ID: Date: Wed, 19 Nov 2025 22:24:25 +0530 Precedence: bulk X-Mailing-List: sched-ext@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched_ext: Fix scx_enable() crash on helper kthread creation failure To: Saket Kumar Bhaskar , sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org Cc: hbathini@linux.ibm.com, sachinpb@linux.ibm.com, tj@kernel.org, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, 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 References: <20251119103722.309211-1-skb99@linux.ibm.com> Content-Language: en-US From: Samir M In-Reply-To: <20251119103722.309211-1-skb99@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=C/nkCAP+ c=1 sm=1 tr=0 ts=691df64b cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=FvzHxZVCrgmYc3naLNIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: xX26GOivM6G9BMhPWME1v2zcBscNtOnK X-Proofpoint-ORIG-GUID: HB7NAfJXeiaNW8Sjh650vvH9hN2bGhAc X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfX6dWjdMoydYrY Q08xO7MN36MUzKvZGyD/4vtD/y/G5akrF/LxfjVo5+uRyfZ45CurYJxLOmzaa2pxnW0vmig/dLQ 0iLzwBi+1iEP5DBp/+wjlZF+vZZ9f+zpExMh5vMkxggOcWrOmF8pRA9jtfWDufOwuPaERMUrjvP Ij7tHDuLyzSv0YMZZa5vIxcB+j1a1mMPQAEm/9st5DGGtXCUu+l2R/FOId4IOsDOcdjf28c9UwC fgACwPVFFRlsPX7yZxqLezx6hutndm+Gqh4IHxg2oLSpUI0O2icRDt5fZQU5vhNiTt2GWsf/AnN AnRa9Ff+xzpm9e8jsXpJQLiqmPd0xaGViLFpha6NDgnwo5xTFgW2s+siywQamzs8oe3JvGHnARf cDHEllZputd9Cjfis8rX//Q6My4eVg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-19_05,2025-11-18_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 spamscore=0 impostorscore=0 bulkscore=0 malwarescore=0 suspectscore=0 clxscore=1011 lowpriorityscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511150032 On 19/11/25 4:07 pm, Saket Kumar Bhaskar wrote: > A crash was observed when the sched_ext selftests runner was > terminated with Ctrl+\ while test 15 was running: > > NIP [c00000000028fa58] scx_enable.constprop.0+0x358/0x12b0 > LR [c00000000028fa2c] scx_enable.constprop.0+0x32c/0x12b0 > Call Trace: > scx_enable.constprop.0+0x32c/0x12b0 (unreliable) > bpf_struct_ops_link_create+0x18c/0x22c > __sys_bpf+0x23f8/0x3044 > sys_bpf+0x2c/0x6c > system_call_exception+0x124/0x320 > system_call_vectored_common+0x15c/0x2ec > > kthread_run_worker() returns an ERR_PTR() on failure rather than NULL, > but the current code in scx_alloc_and_add_sched() only checks for a NULL > helper. Incase of failure on SIGQUIT, the error is not handled in > scx_alloc_and_add_sched() and scx_enable() ends up dereferencing an > error pointer. > > Error handling is fixed in scx_alloc_and_add_sched() to propagate > PTR_ERR() into ret, so that scx_enable() jumps to the existing error > path, avoiding random dereference on failure. > > Fixes: bff3b5aec1b7 ("sched_ext: Move disable machinery into scx_sched") > Reported-by: Samir Mulani > Signed-off-by: Saket Kumar Bhaskar > --- > kernel/sched/ext.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c > index 2b0e88206d07..7fc0cce68a1b 100644 > --- a/kernel/sched/ext.c > +++ b/kernel/sched/ext.c > @@ -4392,8 +4392,11 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops) > goto err_free_gdsqs; > > sch->helper = kthread_run_worker(0, "sched_ext_helper"); > - if (!sch->helper) > + if (IS_ERR(sch->helper)) { > + ret = PTR_ERR(sch->helper); > goto err_free_pcpu; > + } > + > sched_set_fifo(sch->helper->task); > > atomic_set(&sch->exit_kind, SCX_EXIT_NONE); Hi, I have validated this patch using the tools/testing/selftests/sched_ext test suite, and all tests passed without any issues. Thank you for the fix ..!! Please add below tag for the patch set. Tested-by: Samir M Regards, Samir