From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout02.posteo.de (mout02.posteo.de [185.67.36.66]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6EC0548122F for ; Wed, 23 Sep 2026 15:06:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.67.36.66 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790175976; cv=none; b=uDNm2q0DxkahaH2ZPuEf/w9xrMVffVG7ZB9GQZmmLB8korK7Hatgb/Hgz7jKfoSA0QsPSRh5EKAIN4fAkkrakpItXh8Ca8vhU+l+SVtV1VaikNU1iWVVTLQOVfsP3vcOUOSaIXBwtPaMMybIpIk+mYrTxvXaY1Z5JJJjIGzyCqU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790175976; c=relaxed/simple; bh=W8mCp3SJrCu4CBEqSbc4yuvWfyqV1/A4EX/v4gQIyvI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=SyNF6EpwrlDNR/YCviJV+aDeX+h5KnujC486tTY/ZSdtRIHeaPeXRaXTxrAF9dUb6O0pq56Rg3j73TF3hj11ObiVWDIRiI1OPn7tt8bc5m7BJ7kYWOgLFTgLiwdK2jlKRdt7zm48WQ2aAoCjxkip4d9icGGs46/vtkQZZibVpGg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=posteo.de; spf=pass smtp.mailfrom=posteo.de; dkim=pass (2048-bit key) header.d=posteo.de header.i=@posteo.de header.b=dUhDHp1O; arc=none smtp.client-ip=185.67.36.66 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=posteo.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=posteo.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=posteo.de header.i=@posteo.de header.b="dUhDHp1O" Received: from submission (posteo.de [185.67.36.169]) by mout02.posteo.de (Postfix) with ESMTPS id D1A26240101 for ; Wed, 23 Sep 2026 17:06:09 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=posteo.de; s=1984.8680eb; t=1790175969; bh=uEgYgG2jtpKqiEwQEWofsJ4lh37upe+OlrEoikITC34=; h=Message-ID:Subject:From:To:Cc:Date:Autocrypt:Content-Type: MIME-Version:OpenPGP:From; b=dUhDHp1OUpnfUasNBkFTQn3Qy1oMMMERHkE3RzNc9KDn9ean8msh6xLpynV9oGOAp b09yCVlnCBmOwaFbhThbOs+v5JnskGIneGE+ztRMDsSNovkKDIfQXyt+rqezbvv81Q E/0HZ/orNvk33taziSVjvMyYtYX5vc8s7E/5b5qWz7oHr9g1PWfshGY5/krzz9BPUS +CFRtuQxpawTPFuq0pXfRpR2hsxerydyZtnvaGZtY6ioq41T9lk50E2sgMEagyoqz6 G7qg3mDRMvxh/x7gjggiZq8Tgj+eIyjTuWiNGIHLb/Xqewg05xSr84ZD60swSwlIwS QYuSC6cfaSo6A== Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4hqgJs27jgz9rxD; Wed, 23 Sep 2026 17:06:05 +0200 (CEST) Message-ID: <708eb7c004c0cce22d71bc8fbd68b44aa3b704a3.camel@posteo.de> Subject: Re: [PATCH v2 1/3] tty: serdev: Export functions to pause receive_buf callback calls From: Markus Probst To: Gary Guo , Greg Kroah-Hartman Cc: Ayush Singh , Johan Hovold , Alex Elder , 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?= , Eric Biggers , Ard Biesheuvel , Lorenzo Stoakes , Vlastimil Babka , "Liam R. Howlett" , Uladzislau Rezki , Jiri Slaby , "Rafael J. Wysocki" , greybus-dev@lists.linaro.org, linux-serial@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, driver-core@lists.linux.dev Date: Wed, 23 Sep 2026 15:06:08 +0000 In-Reply-To: References: <20260920-rust_serdev_probe_refactor-v2-0-43b855162f5d@posteo.de> <20260920-rust_serdev_probe_refactor-v2-1-43b855162f5d@posteo.de> <2026092356-chatting-dust-3de9@gregkh> <2fcec4f3cd70a41e282505ff5c99b19e5809aead.camel@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="=-qFTq82k4Jz8KYLv/i1pk" Precedence: bulk X-Mailing-List: linux-kernel@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 --=-qFTq82k4Jz8KYLv/i1pk Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2026-09-23 at 14:52 +0100, Gary Guo wrote: > On Wed Sep 23, 2026 at 2:31 PM BST, Markus Probst wrote: > > On Wed, 2026-09-23 at 12:35 +0200, Greg Kroah-Hartman wrote: > > > On Sun, Sep 20, 2026 at 02:29:58PM +0000, Markus Probst wrote: > > > > These functions will be used to simply the serdev rust abstraction.= It > > > > also contributes to the fixing of 2 race conditions in the serdev r= ust > > > > abstraction. > > > >=20 > > > > Signed-off-by: Markus Probst > > > > --- > > > > drivers/tty/serdev/core.c | 50 +++++++++++++++++++++++++= +++++++++++- > > > > drivers/tty/serdev/serdev-ttyport.c | 38 +++++++++++++++++++++++++= +++ > > > > include/linux/serdev.h | 6 +++++ > > > > 3 files changed, 93 insertions(+), 1 deletion(-) > > > >=20 > > > > diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serd= ev/serdev-ttyport.c > > > > index bab1b143b8a6..e8aa89e733bd 100644 > > > > --- a/drivers/tty/serdev/serdev-ttyport.c > > > > +++ b/drivers/tty/serdev/serdev-ttyport.c > > > > @@ -7,8 +7,10 @@ > > > > #include > > > > #include > > > > #include > > > > +#include "../tty.h" > > > > =20 > > > > #define SERPORT_ACTIVE 1 > > > > +#define SERPORT_PAUSE_RX 2 > > > > =20 > > > > struct serport { > > > > struct tty_port *port; > > > > @@ -32,6 +34,14 @@ static size_t ttyport_receive_buf(struct tty_por= t *port, const u8 *cp, > > > > if (!test_bit(SERPORT_ACTIVE, &serport->flags)) > > > > return 0; > > > > =20 > > > > + if (test_bit(SERPORT_PAUSE_RX, &serport->flags)) > > > > + return 0; > > > > + > > > > + /* > > > > + * Ensure writes by the driver are visible before allowing traffi= c to resume. > > > > + */ > > > > + smp_mb__after_atomic(); > > >=20 > > > This scares me. Why not use a real lock?=C2=A0 > > >=20 > > I can use locks to make it less "fragile". But I don't I think I need > > them. > >=20 > > > WHat's the issue here, you > > > need this to be "flushed" before this call: > > >=20 > > > > + > > > > ret =3D serdev_controller_receive_buf(ctrl, cp, count); > > >=20 > > > here? > > >=20 > > > And you just tested a bit, you didn't set a bit, so what are you tryi= ng > > > to ensure is written exactly? > > This should be an acquire load operation (paired with the release store > > operation in `ttyport_resume_rx`). >=20 > Then you should use `test_bit_acquire`. Ok. For some reason there is no equivalent `set_bit_release`. >=20 > However, this isn't sufficient because there's no synchronization between= this > bit test with the bit set inside pause_rx. Will be replaced with a mutex in the next revision. Thanks - Markus Probst >=20 > Best, > Gary --=-qFTq82k4Jz8KYLv/i1pk Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQJPBAABCAA5FiEEgnQYxPSsWOdyMMRzNHYf+OetQ9IFAmqz6twbFIAAAAAABAAO bWFudTIsMi41KzEuMTIsMiwyAAoJEDR2H/jnrUPSOk0QALLiTzfWtOf81gvgqjYo mhW2jo2bqdGVcOHTrqDJY4ms9BRnQmAzJyMamlKEEks3mG6I0QtCAv41lntVXHeW jvcOXO54yyQWxVwS+J+M+y8z//MLdvO7mb5v91vYBEY1jnMwl60PHnuKUuVTLms7 qN+zvihG68OVGFVTInb3CPN4N93cgZkM2gNl+2r/NJxci1tYJN/DgosHvFD2n2UA X1ZkfXBMYxiOClRI5V0M36HL3LNM1tNa7Z32Mvl1D4ym09eUoLhPOT+EPONi65cm WqBwSFQrWwCffcIzetd68CG6G6C9aPjbXValmd3kUAbsxWFdahghADq35wNb1kNE Ga7tcuqL6lpoT46U0wTkDtp8iBk76AjoMK3RtO8SxFxdnstvCVnk8XuqL77QR6tT Fd0lMktEYiCm/prxsbwC9jQqRZNEWMTPKGYr21rU2mClvElu4pRceWwzuxsm8D/i G7T6runz97OxPDxhdjqGdXLtl8yMF6ds8S7/yxx9DqbtzLp+IhZye+HPsstIECWj Xf+ElC8wyTVoCHosvVx6uw1TAKj/mxnq/A2adTvxHYEEiHGOEcMxMENmqZOaKk0G Q1U4Ec9RqiAP9Kri1LPxf0pPmiB7rFHtcpfsd79f4KbLI2Owu/bvxqJ7pEQLLAPo dFPE9V81NqqyfF4mWkx7RIC0 =m2Wa -----END PGP SIGNATURE----- --=-qFTq82k4Jz8KYLv/i1pk--