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Sun, 6 Sep 2026 01:58:59 +0200 (CEST) Message-ID: Subject: Re: [PATCH v4] rust: serdev: Mitigate race conditions From: Markus Probst To: Gary Guo , Miguel Ojeda , Boqun Feng , =?ISO-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , Onur =?ISO-8859-1?Q?=D6zkan?= , Greg Kroah-Hartman Cc: linux-serial@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Sashiko Bot Date: Sat, 05 Sep 2026 23:59:00 +0000 In-Reply-To: References: <20260905-rust_serdev_fix-v4-1-31e1bbcc0c00@posteo.de> Autocrypt: addr=markus.probst@posteo.de; prefer-encrypt=mutual; keydata=mQINBGiDvXgBEADAXUceKafpl46S35UmDh2wRvvx+UfZbcTjeQOlSwKP7YVJ4JOZrVs93 qReNLkOWguIqPBxR9blQ4nyYrqSCV+MMw/3ifyXIm6Pw2YRUDg+WTEOjTixRCoWDgUj1nOsvJ9tVA m76Ww+/pAnepVRafMID0rqEfD9oGv1YrfpeFJhyE2zUw3SyyNLIKWD6QeLRhKQRbSnsXhGLFBXCqt 9k5JARhgQof9zvztcCVlT5KVvuyfC4H+HzeGmu9201BVyihJwKdcKPq+n/aY5FUVxNTgtI9f8wIbm fAjaoT1pjXSp+dszakA98fhONM98pOq723o/1ZGMZukyXFfsDGtA3BB79HoopHKujLGWAGskzClwT jRQxBqxh/U/lL1pc+0xPWikTNCmtziCOvv0KA0arDOMQlyFvImzX6oGVgE4ksKQYbMZ3Ikw6L1Rv1 J+FvN0aNwOKgL2ztBRYscUGcQvA0Zo1fGCAn/BLEJvQYShWKeKqjyncVGoXFsz2AcuFKe1pwETSsN 6OZncjy32e4ktgs07cWBfx0v62b8md36jau+B6RVnnodaA8++oXl3FRwiEW8XfXWIjy4umIv93tb8 8ekYsfOfWkTSewZYXGoqe4RtK80ulMHb/dh2FZQIFyRdN4HOmB4FYO5sEYFr9YjHLmDkrUgNodJCX CeMe4BO4iaxUQARAQABtCdNYXJrdXMgUHJvYnN0IDxtYXJrdXMucHJvYnN0QHBvc3Rlby5kZT6JAl QEEwEIAD4CGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AWIQSCdBjE9KxY53IwxHM0dh/4561 D0gUCaIZ9HQIZAQAKCRA0dh/4561D0pKmD/92zsCfbD+SrvBpNWtbit7J9wFBNr9qSFFm2n/65qen NNWKDrCzDsjRbALMHSO8nigMWzjofbVjj8Nf7SDcdapRjrMCnidS0DuW3pZBo6W0sZqV/fLx+AzgQ 7PAr6jtBbUoKW/GCGHLLtb6Hv+zjL17KGVO0DdQeoHEXMa48mJh8rS7VlUzVtpbxsWbb1wRZJTD88 ALDOLTWGqMbCTFDKFfGcqBLdUT13vx706Q29wrDiogmQhLGYKc6fQzpHhCLNhHTl8ZVLuKVY3wTT+ f9TzW1BDzFTAe3ZXsKhrzF+ud7vr6ff9p1Zl+Nujz94EDYHi/5Yrtp//+N/ZjDGDmqZOEA86/Gybu 6XE/v4S85ls0cAe37WTqsMCJjVRMP52r7Y1AuOONJDe3sIsDge++XFhwfGPbZwBnwd4gEVcdrKhnO ntuP9TvBMFWeTvtLqlWJUt7n8f/ELCcGoO5acai1iZ59GC81GLl2izObOLNjyv3G6hia/w50Mw9MU dAdZQ2MxM6k+x4L5XeysdcR/2AydVLtu2LGFOrKyEe0M9XmlE6OvziWXvVVwomvTN3LaNUmaINhr7 pHTFwDiZCSWKnwnvD2+jA1trKq1xKUQY1uGW9XgSj98pKyixHWoeEpydr+alSTB43c3m0351/9rYT TTi4KSk73wtapPKtaoIR3rOFHLQXbWFya3VzLnByb2JzdEBwb3N0ZW8uZGWJAlEEEwEIADsWIQSCd BjE9KxY53IwxHM0dh/4561D0gUCaIO9eAIbAwULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgAAKCR A0dh/4561D0oHZEACEmk5Ng9+OXoVxJJ+c9slBI2lYxyBO84qkWjoJ/0GpwoHk1IpyL+i+kF1Bb7y Hx9Tiz8ENYX7xIPTZzS8hXs1ksuo76FQUyD6onA/69xZIrYZ0NSA5HUo62qzzMSZL7od5e12R6OPR lR0PIuc4ecOGCEq3BLRPfZSYrL54tiase8HubXsvb6EBQ8jPI8ZUlr96ZqFEwrQZF/3ihyV6LILLk geExgwlTzo5Wv3piOXPTITBuzuFhBJqEnT25q2j8OumGQ+ri8oVeAzx24g1kc11pwpR0sowfa5MvZ WrrBcaIL7uJfR/ig7FyGnTQ1nS3btf3p0v8A3fc4eUu/K2No3l2huJp3+LHhCmpmeykOhSB63Mj3s 3Q87LD0HE0HBkTEMwp+sD97ZRpO67H5shzJRanUaDTb/mREfzpJmRT1uuec0X2zItL7a6itgMJvYI KG29aJLX3fTzzVzFGPgzVZYEdhu4y53p0qEGrrC1JtKR6DRPE1hb/OdWOkjmJ75+PPLD9U5IuRd6y sHJWsEBR1F0wkMPkEofWsvMYJzWXx/rvTWO8N4D6HigTgBXAXNgbc3IHpHlkvKoBJptv6DRVRtIrz 0G0cfBY0Sm7he4N2IYDWWdGnPBZ3rlLSdj5EiBU2YWgIgtLrb8ZNJ3ZlhYluGnBJDGRqy2jC9s1jY 66sLA9rQZMHhJTzMyIDwweGlvMzJAcG9zdGVvLmV1PokCbQQTAQgAVxYhBIJ0GMT0rFjncjDEczR2 H/jnrUPSBQJpa71VGxSAAAAAAAQADm1hbnUyLDIuNSsxLjExLDIsMgIbAwULCQgHAgIiAgYVCgkIC wIEFgIDAQIeBwIXgAAKCRA0dh/4561D0gKJD/9uOQKYlsDoQX65Gd0LiMT0C+5vXgr3VI0PHDOwcv 51fJ3A1vNyPZRFPGrz8+mDEXUQOF/INfnz5Tu1QHwf+iYcWcTGAN/FHgVR6ET6VBNU2hJaKhu+Ggo kjYyJTOvyX+3yNRUfSny0GjTjIPuPTErjqmHF+BtjXslpgwqnNMznf3lRIuUjRORupos6p3k1DndE 5vzUTmXSvMyXyOD2KhBl/kL76k0bHYyAQytZPag12pltrtFbA/r2phDGN2si8PooDT99bSTJjaM45 MTAAHbHKJfvgfK41bNFD5mMtpWpL195XRtS0Nrxdg3PaYBxN5gtTG0RyZfpYRlkdEhm+jj/8RxuSG i/qdhRdbiI7K2IELWeQVHSNDi9JabR/UzlR4NSnhfAjRIVlRM+eFbUl8XwxwVrAkojF5IraH2qRvg VCmuFsHUW07FUlrDrzpjXsD73cKppoFGDCdDR0BHJepXbFLS9+AqkT+guRJlnCTg2p+TQtnbwPgKp Vj98JixovCl99zRYTsL2bRNU5+q8iET65VMJ1ydyNanvLd5vI/NqDkXhlXLsGmdaDTtu4R21PkToX dQNGrZ91M9nlIBKw8Y7c7xZ4098qX2b8JX/CxD+gC1r4C8vuA3GkhFLx+KlkON7LyiJPkrePp6Qky jfGillcaQOqFZ3WwVqyzG1BUfTow== Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-AvUvLUrsSkHeAmTvTL2S" Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 OpenPGP: url=https://posteo.de/keys/markus.probst@posteo.de.asc; preference=encrypt --=-AvUvLUrsSkHeAmTvTL2S Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2026-09-06 at 00:39 +0100, Gary Guo wrote: > On Sat Sep 5, 2026 at 7:47 PM BST, Markus Probst wrote: > > There are currently 2 race conditions: > > - in probe if `Driver::probe` returns Err > > - in unbind > > . In those cases the driver data will be set to NULL before the serdev > > device was closed. If data is received while the driver data is dropped= , > > the `receive_buf_callback` might try to access the `active` mutex on a > > null pointer. The race conditions can only occur if `Driver::receive` i= s > > implemented. > >=20 > > The issue cannot be cleanly fixed without rewriting some logic, which > > might introduce new regressions. > >=20 > > Temporarily disable the use of `Driver::receive`, until fixed in the > > next release. >=20 > Isn't this basically undoing all the usefulness of having the serdev abst= raction > in the first place? It removes 50% of its functionality, so kinda. The initial "synology_microp" driver [1] in the mailing list for instance currently doesn't rely on it (it will need it later though). >=20 > As this is for unbound only, I don't think we need to rush to fix this fo= r rc > anyway. Many C drivers don't get unbind correct (and our misc device). Th= ere's > no in-tree user that will hit this API anyway. Also on probe failure (i.e. Driver returns an error on probe). >=20 > I think we'd better just find a proper fix for the next cycle and leave t= he > current code as is. Thats also an option I wouldn't mind. The proper fix is almost ready. Thanks - Markus Probst [1] https://lore.kernel.org/rust-for-linux/20260724-synology_microp_initial-v18= -0-fb2f49f10e77@posteo.de/ >=20 > Best, > Gary >=20 > >=20 > > Fixes: 99f59aa82341 ("rust: add basic serial device bus abstractions") > > Reported-by: Sashiko Bot > > Closes: https://lore.kernel.org/linux-serial/20260905000836.C8FC91F00A3= D@smtp.kernel.org/ > > Closes: https://lore.kernel.org/linux-serial/20260903222159.70A911F000E= 9@smtp.kernel.org/ > > Signed-off-by: Markus Probst > > --- > > I will submit a patch (for the next merge cycle) soon, which will > > address this issue and make the probe and unbind code less convoluted. > > --- > > Changes in v4: > > - remove comments > > - Link to v3: https://patch.msgid.link/20260905-rust_serdev_fix-v3-1-b8= 6056c3f7a4@posteo.de > >=20 > > Changes in v3: > > - mitigate it > > - Link to v2: https://patch.msgid.link/20260905-rust_serdev_fix-v2-0-35= dfcd06ef2e@posteo.de > >=20 > > Changes in v2: > > - also fix race condition on unbind > > - Link to v1: https://patch.msgid.link/20260905-rust_serdev_fix-v1-1-2e= a92b154a6b@posteo.de > > --- > > rust/kernel/serdev.rs | 6 +++--- > > samples/rust/rust_driver_serdev.rs | 13 +------------ > > 2 files changed, 4 insertions(+), 15 deletions(-) > >=20 > > diff --git a/rust/kernel/serdev.rs b/rust/kernel/serdev.rs > > index 17ca504b7f8d..f4c0f43b5273 100644 > > --- a/rust/kernel/serdev.rs > > +++ b/rust/kernel/serdev.rs > > @@ -148,9 +148,8 @@ fn drop(self: Pin<&mut Self>) { > > =20 > > impl Adapter { > > const OPS: &'static bindings::serdev_device_ops =3D &bindings::ser= dev_device_ops { > > - receive_buf: if T::HAS_RECEIVE { > > - Some(Self::receive_buf_callback) > > - } else { > > + receive_buf: { > > + const_assert!(!T::HAS_RECEIVE); > > None > > }, > > write_wakeup: Some(bindings::serdev_device_write_wakeup), > > @@ -233,6 +232,7 @@ extern "C" fn remove_callback(sdev: *mut bindings::= serdev_device) { > > T::unbind(sdev, data_pinned); > > } > > =20 > > + #[expect(dead_code)] > > extern "C" fn receive_buf_callback( > > sdev: *mut bindings::serdev_device, > > buf: *const u8, > > diff --git a/samples/rust/rust_driver_serdev.rs b/samples/rust/rust_dri= ver_serdev.rs > > index 51b4898cd855..3fd3eef15371 100644 > > --- a/samples/rust/rust_driver_serdev.rs > > +++ b/samples/rust/rust_driver_serdev.rs > > @@ -4,10 +4,7 @@ > > =20 > > use kernel::{ > > acpi, > > - device::{ > > - Bound, > > - Core, // > > - }, > > + device::Core, > > of, > > prelude::*, > > serdev, > > @@ -60,14 +57,6 @@ fn probe<'bound>( > > =20 > > Ok(Self { sdev: sdev.into() }) > > } > > - > > - fn receive<'bound>( > > - sdev: &'bound serdev::Device, > > - _this: Pin<&Self>, > > - data: &[u8], > > - ) -> usize { > > - sdev.write(data).unwrap_or_default() as usize > > - } > > } > > =20 > > impl Drop for SampleDriver { > >=20 > > --- > > base-commit: e5e04726cdd043e309677071ab1b65a4b18f422b > > change-id: 20260904-rust_serdev_fix-be3ff9c8a5e8 >=20 --=-AvUvLUrsSkHeAmTvTL2S Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQJPBAABCAA5FiEEgnQYxPSsWOdyMMRzNHYf+OetQ9IFAmqcrMIbFIAAAAAABAAO bWFudTIsMi41KzEuMTIsMiwyAAoJEDR2H/jnrUPSA5MQAJV8O1pYZJ7MdqoPhC0i HCSFZCLqKeQIDnA8nMdtD4a48gfR5beNCNQwEokjTk1gkQWs69vY1rgS07b877dL uzb3tQC8lnP/RnnbuqOAHgthvhqC8fw/L6ylt4gHrs59K7O73fyGeNXaOvKDEQBl r5KLEJpL49RWQORhegrJpG72d//qDIYpZaF1Jx7zI0LHC0OfODLaB8TwlhbgOjS7 qxLVlB6T+oDgFzRUZksB/8/NRQiI/XR0YNNtXzSx9HeQY+VZzCMSgR2KxvEzojaG eJkd2oigpWFbcY4aTWt1RLyg/dUMVAmt1SwS/DLeS3DS13FkVX5CWOi5QkKIyCh5 9fBjPldCng7jksj5mFTikYzxYcELaQ+IkxUsq44ggJb88V9B3DfzL2IpCeHEPRYM ikQJFQ1FEbafRPOZcWcztIhmpnq/yNZbFD+OF0/brx1kYZ7meiONBWzJ93NL9qnJ HGzg7PJxqCZQe4VUMcVbLmr/osQaPfKr8iU6t0/ku1XM263MlMIO1M+/pJQAKQlJ DHiOnsu5ZIoAPbJfcUXbI3wxwzrCBIfQ0EVX3JdcA2R0FUYAagLeijN9bb0MRMEf YNlI5gJPwcUcSX3VCYQPNTebetFxe8Ap7kdMYclJZTLIMEDI96HRT4kz3nyHq29y LKkseoWVpjHQ9GpJZtcltE8l =IxEx -----END PGP SIGNATURE----- --=-AvUvLUrsSkHeAmTvTL2S--