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McKenney" Subject: Re: [linux-next][s390] Boot hang after merge c50f05bd3c4e (sched/hrtick) Message-ID: <20260305150210.7170D10-hca@linux.ibm.com> References: <28add480-4841-4e6a-a8a9-1211280ecc51@linux.ibm.com> <20260305074922.7170Ad3-hca@linux.ibm.com> <20260305121201.GB596554@noisy.programming.kicks-ass.net> <20260305123505.GA1395416@noisy.programming.kicks-ass.net> <20260305124501.GB1395416@noisy.programming.kicks-ass.net> <20260305130725.GB652779@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-next@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260305130725.GB652779@noisy.programming.kicks-ass.net> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=Rp/I7SmK c=1 sm=1 tr=0 ts=69a99af8 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=kj9zAlcOel0A:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=eh9lVRh74qEsOkDO9VIA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzA1MDExNyBTYWx0ZWRfX+KZ/9ZK13CwP Tlua3Ow3lVoyi+5W7Z4ELcyNBvG8fDTkv+wisEvAUkdGfnmGPSqlXR6wqHadarpwSa4c6Vt0ISq R54c0Kag3ISqo8df94o0a9U1UYNyEchlz8x+O46tcsdEN3iNCHtYS53RhLySrJ/ZvFaD/FavrPm XhrZlVRF9J7ifjBCJEiN8qy7wx7L1xovcquMoqzSzwdxyDwXIrnSVusq4zGpn0FYGtDH1cXbnPh ZeULKVZ4gW5NuF6zPXnF2z8Shs8m1gc1dNy9S78CssIPJGnZQhblnbjMKxuTlbPFlyFA6dSh5rB +6fMylEcf0giYlX9wLYQSGY+1eHMW1dXUKM73lOjynPZ6GK+slpl9Zs5XnkyDXA5n5ki8RNqnr8 OjlfJjwB8rr2B1uqXbzg9ktQhw9Xma3Jr8d+lUuczFa6EwWVrDFPLX45PfvMrSEwEkdDZudzui/ wCvzcVp9/Fxs1btsm1w== X-Proofpoint-GUID: 3Me9obr6uypio5hX8WmI-YawuqHTPKfb X-Proofpoint-ORIG-GUID: 3Me9obr6uypio5hX8WmI-YawuqHTPKfb X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-05_04,2026-03-04_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 priorityscore=1501 spamscore=0 phishscore=0 adultscore=0 bulkscore=0 clxscore=1015 impostorscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603050117 On Thu, Mar 05, 2026 at 02:07:25PM +0100, Peter Zijlstra wrote: > > > Moving that before irq_enter_rcu() means it doesn't see HARDIRQ_OFFSET > > > in preempt_count(). As such, it might actually call into schedule() from > > > hardirq context. > > > > > > Or am I missing something? > > > > N/m, it turns into __this_cpu_add() and that doesn't have > > preempt_enable(). > > > > 00d8b035eb71 ("s390/idle: Slightly optimize idle time accounting") > > > > Is actually a correctness fix afaict. Yes. Those dependencies become quite subtle when calling early into C code. > Another change is that you clear I and E in the PSW bit before > irq_enter_rcu(), which, per: > > 7e641e52cf5f ("softirq: Prepare for deferred hrtimer rearming") > > can re-arm the timer. > > So where previously it would re-arm and still have the I/E bits set, so > the timer could fire, they are now disabled. > > I really don't know if this is a problem; I'm clutching at s390 straws > here that I really don't know much about. That's the old PSW where the interrupt happened, not the one with which the CPU is running with, and shouldn't have any effect. ...but reverting that commit actually does fix it for me. I don't see immediately any code which checks if the _previous_ context had irqs enabled or disabled, since that is the only difference.