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Wed, 5 Aug 2026 07:09:38 +0000 (GMT) Message-ID: <1a6dd561-f529-433d-bc09-094924d861fe@linux.ibm.com> Date: Wed, 5 Aug 2026 12:39:36 +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 v4 05/17] irq & spin_lock: Add counted interrupt disabling/enabling To: Boqun Feng , Peter Zijlstra Cc: Ingo Molnar , Will Deacon , Waiman Long , Gary Guo , Alice Ryhl , Lyude Paul , Daniel Almeida , =?UTF-8?Q?Onur_=C3=96zkan?= , Miguel Ojeda , Danilo Krummrich , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org References: <20260804161447.84806-1-boqun@kernel.org> <20260804161447.84806-6-boqun@kernel.org> <2fc01d90-e081-4ddf-a842-b68eda15ca9e@linux.ibm.com> <20260805063645.GO776954@noisy.programming.kicks-ass.net> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: 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-Spam-Info: AW1haW4tMjYwODA1MDA1MSBTYWx0ZWRfX2Y1RFaos79vm 1Qqj0oE3MAvts7NvrSV3ajdREi5G5w3kAXjZEZ42GYGeUrdQChPf7IHNnsAtax8A1GtK0PoLqwC xCqkfmUHL92TiqqR6kq8C7c9AtGPJm4= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA1MDA1MSBTYWx0ZWRfX2mPDAh6Yt/yF 8iAfCpr6ByCsWk7kMa/5YBGAGbsNdWs7yuhVanVMfZ6jjCz05xGeMD+nuxciiq9OVHEQEssDTkD 8oMQyq3H5GrcfU8P5qEpWE0mR3lcrKk3OTNGt0SzGVIdu3ZgLwNcieY3AyK/9yfNFHnzhTaOtWP 6gdZuRDvShWxJm874+Md7a2dlFM1u85bzUjQgIAxRppUp8yLvWwt96Oa1JGmU2JRs6z2Dmj055J 4fipt6N1qAe7Hv7ueFC3XwBvKUJowyhMB+cBpDVxeMJntEDVP0QfD1tvBs3B9L7UNWXh1Wk4IXf 67qjS5O3vl4Lr6EO0x5EDwOAbmF1YHu+upDFSCRkKFsgZ6JQJqYuajOA+1aj4Ak4GD8jpDs+dpu 2Ulaf1WhLdVKi0PNF6MkNMvTtR/xn533MhF+g8pwjcDcXRLrsiv84APPIHiqwhLO20OX9oV/x4J BU5qkuQYShNBXIa078g== X-Authority-Analysis: v=2.4 cv=SI1ykuvH c=1 sm=1 tr=0 ts=6a72e1bc cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=1piVZe82tsHeqK_2eX4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: n308oW4qHgKqrmwJSbP7DRyitp7lugLB X-Proofpoint-GUID: AzzTBLHlUffgZCZvF9VtR4XH5GmeCHqS X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-05_02,2026-08-04_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 bulkscore=0 suspectscore=0 impostorscore=0 spamscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608050051 On 8/5/26 12:37 PM, Boqun Feng wrote: > On Wed, Aug 05, 2026 at 08:36:45AM +0200, Peter Zijlstra wrote: >> On Tue, Aug 04, 2026 at 02:08:11PM -0700, Boqun Feng wrote: >> >>>>> + /* Interrupts can happen here, but it's OK, see __irq_exit_rcu(). */ >>>>> + >>>>> + if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET) >>>>> + _local_interrupt_disable(); >>>>> +} >>>> >>>> Maximum nesting possible is 256 right? Whats is stopping here to do more than that? >>> >>> Yes. Currently similar as softirq, we don't detect the overflow. >>> >>>> Should there be a warn_on? >>> >>> A simple warn_on could be problematic because warn_on() itself may take >>> an irq-disabling lock, and that may trigger another overflow on top of >>> the existing overflow. It's a bit tricky to do a proper detection. But >>> I'm open to ideas. >> >> DEBUG_PREEMPT's preempt_count_add() does: >> >> DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >= PREEMPT_MASK - 10); >> > > Yeah, but this is behind a kconfig (DEBUG_PREEMPT), so not sure whether > it's what Shrikanth asked here. > I was suggesting to have a mechanism which allows to debug it/ find the callers. > Regards, > Boqun > >>