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Mon, 29 Jun 2026 06:04:03 +0000 (GMT) Received: from [9.123.7.57] (unknown [9.123.7.57]) by smtpav05.wdc07v.mail.ibm.com (Postfix) with ESMTP; Mon, 29 Jun 2026 06:04:03 +0000 (GMT) Message-ID: <86244af7-268b-45f3-a8a1-e94ae1923ca9@linux.ibm.com> Date: Mon, 29 Jun 2026 11:34:01 +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: [PATCHv2 05/17] nvme: add Clang context annotations for nvme_ns_head::current_path To: Marco Elver , paulmck@kernel.org Cc: Christoph Hellwig , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, kbusch@kernel.org, sagi@grimberg.me, axboe@fb.com, bvanassche@acm.org, gjoyce@linux.ibm.com References: <20260614131541.2017845-1-nilay@linux.ibm.com> <20260614131541.2017845-6-nilay@linux.ibm.com> <20260626064050.GE10731@lst.de> <41a4cb5a-077c-499f-b060-2a4263303350@paulmck-laptop> <62bbec8e-6eb5-4024-acba-6be1e7f33080@paulmck-laptop> Content-Language: en-US From: Nilay Shroff 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-GUID: 22JtMsD6j39KfnoqKoP6cHzufmuOWnqr X-Proofpoint-Spam-Info: AW1haW4tMjYwNjI5MDA0NyBTYWx0ZWRfX7bgb91GGQryo EIJrQCTVmt3/Yy3gqa17TSempWCJGH2yu0AfwV0CVvqd+xCm4ACNRYeP2ipDvqi5bAxJ3fMaEpE wlC1OoTmWg+roeazO0HOnfEKcvZNma0= X-Authority-Analysis: v=2.4 cv=edsNubEH c=1 sm=1 tr=0 ts=6a420ad9 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=6P4JVspCszbSNExKLKAA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjI5MDA0NyBTYWx0ZWRfX+UxsxIBKSQI7 hu8gz82J+Wr4Jp2lMkdzovE6OTJo4xqgGNqCe9K1F/2qz2JNnUmMbQnBWnrmQC+c1RfaH4UBR70 5b7fB+szcOKdLZVE6Y/dZWRp5G2Oo9Uo1dGU+CDX9miRNcIKX0jlAARpNNt67KVJaUZpNpfE7RP Ei/xnbXMnj/t5uDgrk1htLFC+ydTRJ2JHGS2rnifH5I3o4NdbgiaIVrLwOS31KMZE9n2cJ9HPiu +lLSU4KaTd+dJqpKHwim9Z6sMzGC30q6A4d6XbuknzO2piQpmywJTgmxS/DgYZP/j6NbsGaA2Kd PkOJIylry0X12h1ZJ7tcR6rqN2S4A5A+4FknwSFCcRWK1u2Yl5srOXAvwAoYEkFWv/Zwb4ORFLe zE8YCqPSrKoroaj+pWoHHxWInIC7dKOWA3P8HfGv1TSvIFhHzzZSmDOMEw4dyvttUyY9sVkKPW/ BDru047r3CXoC2F9fIg== X-Proofpoint-ORIG-GUID: tTsSgPbcE_ubEQbp56dd6syL7Grf86nk X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-29_01,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 adultscore=0 impostorscore=0 bulkscore=0 spamscore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606290047 On 6/29/26 11:30 AM, Marco Elver wrote: > On Sun, 28 Jun 2026 at 18:07, Paul E. McKenney wrote: >> >> On Sun, Jun 28, 2026 at 08:00:00AM +0200, Marco Elver wrote: >>> On Sat, 27 Jun 2026 at 19:14, Paul E. McKenney wrote: >>>> >>>> On Sat, Jun 27, 2026 at 05:38:44PM +0200, Marco Elver wrote: >>>>> On Fri, 26 Jun 2026 at 20:36, Paul E. McKenney wrote: >>>>>> On Fri, Jun 26, 2026 at 08:40:50AM +0200, Christoph Hellwig wrote: >>>>>>> On Sun, Jun 14, 2026 at 06:45:20PM +0530, Nilay Shroff wrote: >>>>>>>> +++ b/drivers/nvme/host/multipath.c >>>>>>>> @@ -231,8 +231,16 @@ bool nvme_mpath_clear_current_path(struct nvme_ns *ns) >>>>>>>> bool changed = false; >>>>>>>> int node; >>>>>>>> >>>>>>>> + /* >>>>>>>> + * This helper is used by namespace failover/teardown and I/O policy >>>>>>>> + * update paths. We only compare the head->current_path[] pointer value >>>>>>>> + * and do not dereference the referenced namespace, so suppress the >>>>>>>> + * context analysis warning for this lockless inspection of the >>>>>>>> + * __rcu_guarded pointer. >>>>>>>> + */ >>>>>>>> for_each_node(node) { >>>>>>>> - if (ns == rcu_access_pointer(head->current_path[node])) { >>>>>>>> + if (context_unsafe(ns == >>>>>>>> + rcu_access_pointer(head->current_path[node]))) { >>>>>>> >>>>>>> I think we need a helper for this, as for a simple pointer value >>>>>>> comparison without a dereference we don't really need either >>>>>>> rcu_access_pointer nor locking. >>>>>>> >>>>>>> Maybe somthing like a >>>>>>> >>>>>>> rcu_compare_pointer(rcu_pointer, nonrcu_pointer) >>>>>>> >>>>>>> ? >>>>>> >>>>>> We could provide something like this: >>>>>> >>>>>> #define rcu_compare_pointer(rcu_pointer, nonrcu_pointer) \ >>>>>> context_unsafe(rcu_access_pointer(rcu_pointer) == (nonrcu_pointer)) >>>>>> >>>>>> Or maybe rcu_pointer_equals()? >>>>>> >>>>>> Marco, thoughts? >>>>> >>>>> I see 2 options: >>>>> >>>>> 1. rcu_compare_pointer / rcu_pointer_equals as proposed. It's more >>>>> explicit but does add some friction during Context Analysis >>>>> enablement. But this only makes sense if there are cases where >>>>> rcu_access_pointer() should be used under the RCU reader lock, which >>>>> led me to the next suggestion... >>>>> >>>>> 2. Redefine rcu_access_pointer() to just not require the RCU read-side >>>>> lock to be held as: >>>>> >>>>>> #define rcu_access_pointer(p) context_unsafe(__rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)) >>>>> >>>>> [ Or alternatively wrap __rcu_access_pointer() in context_unsafe() >>>>> (similar to rcu_assign_pointer and friends). ] >>>>> >>>>> I think rcu_access_pointer() is in the same category as the other RCU >>>>> pointer helpers, although currently only the pointer update helpers >>>>> imply context_unsafe(); I think it might have been an oversight >>>>> initially, and we should change rcu_access_pointer() to match. There >>>>> should be no reason why an rcu_access_pointer() should be protected by >>>>> the RCU read-side critical section, since it's not meant for >>>>> dereferencing the pointer (that'd be a bug; its documentation also >>>>> says "Return the value of the specified RCU-protected pointer, but >>>>> omit the lockdep checks for being in an RCU read-side critical section >>>>> [...]"). >>>>> >>>>> If you agree there should be no cases where an rcu_access_pointer() >>>>> should be guarded by an RCU read-side critical section, then I think >>>>> this is the simplest and correct design, and avoids expanding the RCU >>>>> API. >>>> >>>> I don't know of any uses of rcu_access_pointer() within an RCU read-side >>>> critical section, but code in a function that might be called both within >>>> and outside of a critical section might well use rcu_access_pointer(). >>>> In other words, it should be OK to use rcu_access_pointer() within an >>>> RCU read-side critical section as well as outside of one. >>> >>> Thanks, yes, that's what I wanted to confirm; i.e. it's ok to use >>> rcu_access_pointer() within and outside an RCU read-side critical >>> section. >>> >>> In which case, my proposal (2) to make rcu_access_pointer() not warn >>> on accessing __rcu_guarded pointers outside an RCU read-side critical >>> section should be the simpler and more generic change (vs. adding a >>> new rcu_pointer_equals() helper). >> >> As shown below? >> >> My guess is that this change makes it unnecessary to have a separate >> RCU-protected-pointer comparison macro, but please let me know if I am >> missing something. > > Looks good to me. Yes, this makes a new comparison macro unnecessary. > > Nilay, does this work and simplify the patch for you? Yeah, this work for me. In fact, I have already tested this patch from Paul and sent my Tested-by tag[1]. You may have missed it. [1] https://lore.kernel.org/all/2a3c6a56-a9a6-461e-80ca-c0f2b4203bff@linux.ibm.com/ Thanks, --Nilay