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McKenney" 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> <20260305150210.7170D10-hca@linux.ibm.com> Content-Language: en-US From: Mikhail Zaslonko In-Reply-To: <20260305150210.7170D10-hca@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: N2TvqY9IMQqgqq70Y0Q9xGSR3M8mD1yp X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzA1MDE0MCBTYWx0ZWRfXxlLuEiY9WvcO kyVjn1RtVgzn3VDJRAU+jnQvzBKYyki0HlEXzwuwyevypXYiB4AggnN1sHbYTt1woCNIPXYKXQ0 BDkI0GIdYZEbk2OGTd5N5TYjN+lpNpJlWf7VdBLdSLduwIqZ5ObgJc+xUnH4iIkrkSB+ODmS6dg O3W/hIs+5Wb3yaTon3XxdZBGXs5iO9pllHItNYTpFBs1S3VvcjP2NxwZjnW7vr/S1QOR6Laua1+ jTofd1outRazoDpkP2VHgFObflv2ICc28yosckyuKXx+oaDtN4JfXYO6VnY0VgUj9v0XMdc69gb cM/LAyvSPnCyZfBv/G36h+lvqjr53qULpO+dFuQTi61OVCxGKUFnzAKIJ1ZEcN6JZ/qr09+Lbn1 bssi9Qwb8SxoqR1P9KkhXvzLAd65yXr4gehS7BLuCCYuwRww70/2qdvxHTZKv5fSPj9pg18Y+id S+4BgtH6/svqyZMCqrw== X-Authority-Analysis: v=2.4 cv=csCWUl4i c=1 sm=1 tr=0 ts=69a9bc66 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=XzDXOgBD491ubj_CJSkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: N2TvqY9IMQqgqq70Y0Q9xGSR3M8mD1yp 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_05,2026-03-04_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 priorityscore=1501 suspectscore=0 malwarescore=0 adultscore=0 clxscore=1011 bulkscore=0 phishscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603050140 On 05-Mar-26 16:02, Heiko Carstens wrote: > 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. For me it doesn't. But reverting this one helps: 15dd3a948855 ("hrtimer: Push reprogramming timers into the interrupt return path")