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[212.8.243.115]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483c3b770c2sm281641905e9.10.2026.03.02.07.11.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Mar 2026 07:11:38 -0800 (PST) Message-ID: <4369c322cd0626844ace0f42c55ec2cd9890cda0.camel@redhat.com> Subject: Re: [PATCH v6 15/16] rv: Add deadline monitors From: Gabriele Monaco To: Juri Lelli Cc: linux-kernel@vger.kernel.org, Steven Rostedt , Nam Cao , Juri Lelli , Jonathan Corbet , Masami Hiramatsu , linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Peter Zijlstra , Tomas Glozar , Clark Williams , John Kacur Date: Mon, 02 Mar 2026 16:11:36 +0100 In-Reply-To: References: <20260225095122.80683-1-gmonaco@redhat.com> <20260225095122.80683-16-gmonaco@redhat.com> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== User-Agent: Evolution 3.58.3 (3.58.3-1.fc43) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: EKSa5EUe46Ooq8g6ItPhIBY4T65Buc-ecxCRhatVigE_1772464300 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2026-03-02 at 15:37 +0100, Juri Lelli wrote: > > +=09if (!pid) > > +=09=09*p =3D current; > > +=09else { > > +=09=09/* > > +=09=09 * Required for find_task_by_vpid, make sure the caller > > doesn't > > +=09=09 * need to get_task_struct(). > > +=09=09 */ > > +=09=09guard(rcu)(); > > +=09=09*p =3D find_task_by_vpid(pid); > > +=09=09if (unlikely(!*p)) > > +=09=09=09return -EINVAL; > > +=09} >=20 > Not sure I get this comment. RCU is released when the function returns, > but then the task pointer is dereferenced by callers? The idea was that the caller should ensure there's no need to do get_task_struct() (which is fine within the syscall, I'm assuming). But looking at it again, that's not even necessary as long as the caller lo= cked RCU, which they should do instead of guarding here. So yeah, the comment is misleading and I should just do: guard(rcu)(); extract_params(...); Thanks for the observation, Gabriele