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Tue, 11 Aug 2026 07:43:35 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel-mentees@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 11 Aug 2026 11:43:29 -0300 Message-Id: Cc: "Alexandre Courbot" , "Alice Ryhl" , "Andreas Hindborg" , "Benno Lossin" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Boqun Feng" , "Daniel Almeida" , "Danilo Krummrich" , "Miguel Ojeda" , =?utf-8?q?Onur_=C3=96zkan?= , "Shuah Khan" , "Tamir Duberstein" , "Trevor Gross" , , , , "Sashiko" Subject: Re: [PATCH] rust: i2c: avoid locking when calling I2cAdapter::inc_ref From: =?utf-8?q?Nicol=C3=A1s_Antinori?= To: "Igor Korotin" , "Gary Guo" X-Mailer: aerc 0.20.0 References: <20260615201141.8920-1-nico.antinori.7@gmail.com> <178628144572.5226.7072490581990266256@linux.dev> In-Reply-To: <178628144572.5226.7072490581990266256@linux.dev> On Sun Aug 9, 2026 at 10:17 AM -03, Igor Korotin wrote: > Hello Nicol=C3=A1s > > Sorry for the delay. > > Yes, worth fixing regardless of real users -- inc_ref taking a lock it > doesn't need is a real bug, not speculative work. > > Instead of adding a separate Rust-only wrapper, please consider splitting > i2c_get_adapter itself: pull the increment into a helper, export it, and > call it directly from inc_ref -- no lock, no lookup: > > +bool __i2c_adapter_get(struct i2c_adapter *adapter) > +{ > + if (try_module_get(adapter->owner)) { > + get_device(&adapter->dev); > + return true; > + } > + return false; > +} > +EXPORT_SYMBOL(__i2c_adapter_get); > + > struct i2c_adapter *i2c_get_adapter(int nr) > { > struct i2c_adapter *adapter; > > mutex_lock(&core_lock); > adapter =3D idr_find(&i2c_adapter_idr, nr); > - if (!adapter) > - goto exit; > - > - if (try_module_get(adapter->owner)) > - get_device(&adapter->dev); > - else > + if (adapter && !__i2c_adapter_get(adapter)) > adapter =3D NULL; > - > - exit: > mutex_unlock(&core_lock); > return adapter; > } > EXPORT_SYMBOL(i2c_get_adapter); Excellent! Thank you for this suggestion and the explanation! > > Heads up for v2: Trevor Chan has a patch changing AlwaysRefCounted::inc_r= ef > to an associated function (fn inc_ref(obj: &Self)). Not merged yet -- > rebase onto it if it lands first. I think it is better to wait until Trevor Chan's patch gets merged since it is in v7 [1] and already has been reviewed by some mantainers. If I send= =20 this fix and gets merged first he will probably have conflicts and have to send a v8. I'll keep an eye on the progress of that patch and once it is merged I am going to send this fix. Thank you, Nicol=C3=A1s [1] https://lore.kernel.org/rust-for-linux/20260628100731.64885-1-trev@trev= rosa.dev/T/#u