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Wed, 12 Mar 2025 11:35:49 -0700 (PDT) Received: from [192.168.10.81] ([176.206.122.167]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-43d0a8d068esm28753615e9.33.2025.03.12.11.35.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Mar 2025 11:35:48 -0700 (PDT) Message-ID: Date: Wed, 12 Mar 2025 19:35:46 +0100 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] ipmi: fix suspicious RCU usage warning To: paulmck@kernel.org, Rik van Riel Cc: Corey Minyard , openipmi-developer@lists.sourceforge.net, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20250312131932.44d901f7@fangorn> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/12/25 18:29, Paul E. McKenney wrote: > On Wed, Mar 12, 2025 at 01:19:32PM -0400, Rik van Riel wrote: >> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c >> index 1e5313748f8b..a2823763fd37 100644 >> --- a/drivers/char/ipmi/ipmi_msghandler.c >> +++ b/drivers/char/ipmi/ipmi_msghandler.c >> @@ -1235,7 +1235,7 @@ int ipmi_create_user(unsigned int if_num, >> return -ENOMEM; >> >> index = srcu_read_lock(&ipmi_interfaces_srcu); >> - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { >> + list_for_each_entry_srcu(intf, &ipmi_interfaces, link) { > > Doesn't the above line want to be something like this? > > + list_for_each_entry_srcu(intf, &ipmi_interfaces, link, > srcu_read_lock_held(&ipmi_interfaces_srcu)) { Ouch what a mess. There are multiple occurrences of this, almost all susceptible to the same warning. I'd start with: -#define ipmi_interfaces_mutex_held() \ - lockdep_is_held(&ipmi_interfaces_mutex) +#define for_each_ipmi_interface(intf) \ + list_for_each_entry_srcu(intf, &ipmi_interfaces, link, + srcu_read_lock_held(&ipmi_interfaces_srcu) + || lockdep_is_held(&ipmi_interfaces_mutex)) { and use the for_each_ipmi_interface() macro throughout the file. Here is the list... all of them are using _rcu, plus: - ipmi_smi_watcher_register is using the wrong lockdep_is_held() assertion, but would warn if fixed - ipmi_add_smi is using _rcu but otherwise correct - ipmi_get_smi_info is using _rcu and can warn - ipmi_timeout is using _rcu and can warn - panic_event is using _rcu and can warn, and is also not using any protection around the walk. Taking srcu_read_lock would be much better On top of this, intf->users_srcu never does a synchronize_srcu, so I'm a bit at a loss at how it is protecting the list. The safest change here is probably: diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c index f2a56c624f54..dc8936254c1b 100644 --- a/drivers/char/ipmi/ipmi_msghandler.c +++ b/drivers/char/ipmi/ipmi_msghandler.c @@ -3769,12 +3769,12 @@ void ipmi_unregister_smi(struct ipmi_smi *intf) intf->in_shutdown = true; list_del_rcu(&intf->link); mutex_unlock(&ipmi_interfaces_mutex); - synchronize_srcu(&ipmi_interfaces_srcu); /* At this point no users can be added to the interface. */ device_remove_file(intf->si_dev, &intf->nr_msgs_devattr); device_remove_file(intf->si_dev, &intf->nr_users_devattr); + synchronize_srcu(&ipmi_interfaces_srcu); /* * Call all the watcher interfaces to tell them that ... plus replacing all uses of intf->users_srcu with ipmi_interfaces_srcu. A couple more issues: - in handle_read_event_rsp() there's a lone rcu_read_unlock() that should become srcu_read_unlock() (currently for intf->users_srcu; modulo changes like the above) - while the intf->cmd_rcvrs list is protected by regular RCU, there are many other occurrences of rcu_read_lock(), typically followed by if (intf->in_shutdown) { rv = -ENODEV; goto out_err; } and I think they should use interfaces_srcu instead. Paolo >> if (intf->intf_num == if_num) >> goto found; >> } >> -- >> 2.48.1 >> >