From owner-freebsd-hackers@freebsd.org Mon May 20 15:38:22 2019 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id ADF1215B06B3; Mon, 20 May 2019 15:38:22 +0000 (UTC) (envelope-from lev@FreeBSD.org) Received: from smtp.freebsd.org (smtp.freebsd.org [96.47.72.83]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "smtp.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 1639F8392F; Mon, 20 May 2019 15:38:22 +0000 (UTC) (envelope-from lev@FreeBSD.org) Received: from onlyone.not-for.work (onlyone.not-for.work [148.251.9.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) (Authenticated sender: lev/mail) by smtp.freebsd.org (Postfix) with ESMTPSA id B605E1CE0A; Mon, 20 May 2019 15:38:21 +0000 (UTC) (envelope-from lev@FreeBSD.org) Received: from [192.168.23.186] (unknown [89.113.128.32]) (Authenticated sender: lev@serebryakov.spb.ru) by onlyone.not-for.work (Postfix) with ESMTPSA id 96B86186AD; Mon, 20 May 2019 18:38:19 +0300 (MSK) To: freebsd-fs@freebsd.org, freebsd-hackers@FreeBSD.org, Alexander Motin Reply-To: lev@FreeBSD.org From: Lev Serebryakov Subject: Commit r345200 (new ARC reclamation threads) looks suspicious to me. Openpgp: preference=signencrypt Autocrypt: addr=lev@FreeBSD.org; prefer-encrypt=mutual; keydata= mQINBFKbGksBEADeguVs+XyJc3mL3iiOBqDd16wSk97YTJYOi4VsHsINzJr09oFvNDiaDBIi fLn2p8XcJvehcsF2GSgrfXfw+uK4O1jyNIKJmiYA0EtE+ZbRtvDrrE0w6Q8+SDeKA21SWh3Y vSQ0DJUontbgW55ER2CbEiIUTIn34uQ0kmESAaw/v5p/9ue8yPTmURvv130FqPFz8VPzltqL NxyGt54TxPfKAzAHEIwxlEZ63JOwzloKh1UDBExcsf9nJO08/TAVgR5UZ5njFBPzaaquhRoP qPJLEQQDqxPIlvMNtHKf7iIebE4BHeqgCdJA0BoiR6gpa0wlsZtdrTPK3n4wYSphLvGbhfOZ YW/hbcu7HYS/FImkVxB3iY17kcC1UTnx4ZaYeASPBGOOPbXky1lLfmDGWIFT//70yx+G17qD OZzF1SvJJhGvh6ilFYaWMX7T+nIp6Mcafc4D7AakXM+XdubNXOMlCJhzPcZ0skgAEnYV587w V7em5fDVwQccwvtfezzqKeJAU5TGiywBHSR5Svzk2FwRNf6M//hWkpq0SRR63iOhkHGOAEBi 69GfEIwH2/w24rLxP0E+Hqq8n+EWNkPatw1Mhcl5PKkdvGCjJUaGNMkpBffjyYo254JXRscR eEnwdIkJt4ErDvjb2/UrOFq31wWMOiLzJeVchAgvTHBMRfP9aQARAQABtCFMZXYgU2VyZWJy eWFrb3YgPGxldkBGcmVlQlNELm9yZz6JAlYEEwEIAEACGwMHCwkIBwMCAQYVCAIJCgsEFgID AQIeAQIXgBYhBPltHKC19DGLZ0szCuqwPFi/3EePBQJb/TeXBQkPBbfGAAoJEOqwPFi/3EeP LtEQANQLS89OCDSnLDZLyCj7sH5GZbTikJp9Or2McqEOpjgtfY/OgqCe7lfo8f71tTN3gL2t VGtNEtsl6CqKeBdm6fqsetCAed2+waJfbXLZWReLRSFQJ/cbof8MB3h/uEw8Zng1ZbyEU0eG rc41Mhk8bTfxjNRjkXDbp0+2xug+eRr2RYhiY2SxH+iy57AbRIu9gkjfL05VztfvsV5dPxt7 +reHf2Vhtu+qCRtCytGQqDvYWGpVZ8U5fHJxFdsJpn66LAe8w+iRGCbppB5TKeHkqWqDb++u sd5ZHzwep/7qcLBeKggi8+a2C3J1J4TpYBwdPgusrGtBPf2EYSTc/0mW5j86g1l8UDN9qXAI FvWbKf22p5SlYUzf5qRLny4ZdDl1mH13lmJV7ZkZGMKnt0IjJ2x0LRgLGhiSm/D4Lh8yc/MX uhj9BB020XbWcMUPpA7S7YaWeIXbnK3NrPU0yk77prFJblfskOwuaxJIwa2mX+cCAQA95As5 2talifo4Kh8OLSvS1gpbMo64LllTzuGbCWuKecH3fpMlZlD7/10z9lBvkSXA7KgadDfN0yHO xGCK8KE9gXXmEVRlbgGDYOJw9FLWHuSZHUvQTkmr4goXrmMIKa9A4BKO3s9vowP4pJ0vp3kz MIBeEwKSvAeZZfgKbIKggKUuQ5gsAqvF360sG3+UuQINBFKbGksBEAC0a9wfjo2P3JyT7Lc+ QlbFVshGbSbazb4ma7QYG5IZZD5vfLBFkePoG6cnrn3WCXp4A43hszAynCwe4eXyAkv4+gPF 3ZSeNE5Wz3zYG+jh2nm2iGCkyaVykfbA+2chor2DKH5tHpuNMBlF+wSJHZKJmlo/sFIktAnV 1NBVg4/cL+9/hIpvl82cl3hYCD7/e7/qRE+w38CpAAzn65FvbODn7xlY3fsJt+cHPBJ4EBM9 KnTwcce+F+72RQMZQEl7vIAwSRmLdgZHN0MFC533l62SVoKjT0eaOOIBrvesmojhWjfwugib Xr+WRF/tGcW77Bxwe2eQLbEVESqWeMORxRxocx7Q7aACoHmf4G4U1Vzx7zUEfNfHjfjZeQVf AURf/MoUelZSW/BmMIfKCg3lRlWAt+Pq2h2UADPVqAZze45beE/c8z8LZsOZiGoRhYL8NSg6 +ziLTdmYLWdtFGAuZhqOtNp5h6tGj21OksBotcaIa5YjbCmmnImIjGlSBkUKvIhq/RXth5b2 gNwaQdu+Yv4AlZVHRsuVywL/skDFL5+We11bDK6MQ5PzvmntRJcgbyoisn1hiV04OV1LpJJM kJn1j8VlBqDQNT/z+BjB0ru/0anv+5uLj7v0ck06rEo4yiXT/ZAcBM76j7V7FaGbkoba6bUU CQ2H5YYBOKpikjCnpwARAQABiQI8BBgBCAAmAhsMFiEE+W0coLX0MYtnSzMK6rA8WL/cR48F Alv9N7IFCQ8Ft+cACgkQ6rA8WL/cR49wpw//W7QrZHKYUWEVHtPLVMlcM1f7MgwnYlIRe/I6 gykwvt87sqxSYu7eHxfX6JZR2M9UYuUYscSR57gxXKu2Uzqaz2KjvEIXJCwCTsuXZjkQ19oL hAPsucw2AcMI6YqPXbZ7hO0Mh8jMeJzD6vDvx3zvunQxGQoZKxr3BvRUyO7NCYbA7N8ccI3E Tmdjj9JTbtue9WaUeGLszFDiITmkASBdsK07y4ylLAJzUGCvYLBU3gx0bBOB2S8SbxHYmQlj ewjovbp+MbT+CoXNxZp+gDRModGyIMdRIotkRiDbgNl0VWIT0SS1GUUlUHKzQ/ZPUvpvk6Gq s/SYBS7rBQNSoXXmJxNW6I6atVNW7JhInC1tkHxBlbpik4FK07J6NHFTx+9ygyCxbxwNA/Le FGkL3kU0VFXR2dNiAVbeueUPF6tU5Bye5ftgpLKOSAbo1g++EKUkc8335/4oYRBMcGEk4xUr NAvzoFPhA2W3KtklruJ9ThrFt9+//NB5ySlVgTwGWMuBJoskEmNOTBv34/UQPUIuE4xSwy6y H+nRQJooiMFo5QCosslJPlwyV63NS9lYXB6n3QWOCP6sFdWACNUCOFv4uk7LQdY9BsCmt2Tk cLuHmoS+fvUesQXnYV2aQi9HciriPIj2gvJ6WjgiaC/PpePil0fzyrfG/JMyHL0qcgmYoj0= Organization: FreeBSD Message-ID: <55989579-a228-498e-2842-453cad6f315f@FreeBSD.org> Date: Mon, 20 May 2019 18:38:07 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="2otz2YBkNKpHdJOidjhGzRvIgUzq6EAGT" X-Rspamd-Queue-Id: 1639F8392F X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org X-Spamd-Result: default: False [-2.98 / 15.00]; local_wl_from(0.00)[FreeBSD.org]; NEURAL_HAM_MEDIUM(-1.00)[-0.999,0]; NEURAL_HAM_SHORT(-0.98)[-0.983,0]; ASN(0.00)[asn:11403, ipnet:96.47.64.0/20, country:US]; NEURAL_HAM_LONG(-1.00)[-1.000,0] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 20 May 2019 15:38:23 -0000 This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --2otz2YBkNKpHdJOidjhGzRvIgUzq6EAGT Content-Type: multipart/mixed; boundary="vr8o0Z3UyUbX9pqkufPdmsagmN2NSX6yY"; protected-headers="v1" From: Lev Serebryakov Reply-To: lev@FreeBSD.org To: freebsd-fs@freebsd.org, freebsd-hackers@FreeBSD.org, Alexander Motin Message-ID: <55989579-a228-498e-2842-453cad6f315f@FreeBSD.org> Subject: Commit r345200 (new ARC reclamation threads) looks suspicious to me. --vr8o0Z3UyUbX9pqkufPdmsagmN2NSX6yY Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable I'm looking at last commit to 'sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c' (r345200) and have one question. Is it Ok for two threads to communicate via simple global variable? Now new code has (line 315): static boolean_t arc_adjust_needed =3D B_FALSE; And after that some threads run code like this: mutex_enter(&arc_adjust_lock); arc_adjust_needed =3D B_TRUE; mutex_exit(&arc_adjust_lock); zthr_wakeup(arc_adjust_zthr); And thread `arc_adjust_zthr` has code like this (line 4874): return (arc_adjust_needed); This variable is not atomic. It is not updated and/or read in atomic way. What code gives guarantees that `arc_adjust_zthr` will detect this change? I don't see any. Am I wrong? --=20 // Lev Serebryakov --vr8o0Z3UyUbX9pqkufPdmsagmN2NSX6yY-- --2otz2YBkNKpHdJOidjhGzRvIgUzq6EAGT Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE+W0coLX0MYtnSzMK6rA8WL/cR48FAlziyd9fFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEY5 NkQxQ0EwQjVGNDMxOEI2NzRCMzMwQUVBQjAzQzU4QkZEQzQ3OEYACgkQ6rA8WL/c R48yvxAApPXpt46m0ejunWWcU6ul4k4m+c0UvPn3AbQuS6DB1gHcAY4lOyTe0XTy xOsl3JJD3CYyK3IGjFt29WqrPSbZzRGR7Jxew/mS9alJztElkCVGfPZccJkf2sJo WxBwJAv0zERVJM6tlml3E+8gjS0IJje0Own2zSHUOorv6c+uXQhQQTC1G+EYdEnY lmghAf105yi8ur0HSCadp0jSlGZ+RWLc/RDldQMCPnNdLLl8xKjAxnaOSCPsaOXn vDZ5OWinQBtCQtMk4eBhFxXhWiBUzOEYMYYy6PJWfmVMfsIodrx8Vakx2J4GeVXl lLPuvc0Xiftp94ya6C7FdIUiuxktDixo0571EFMNQqUrJTxTAVOtKkCC4KCzEnZt Eb3f8Uk0Mrdn2GW0ML/0Dr0jzXw6SzyaApsH9LO1twCAtVj6VTGJA1j9yTHljbeS D7CusKEETGuE8/We/ni7V7x2sLAsXH5HyLBdYVwNRGRLFWdEIINH6yNZnHS893+K ZzWLWfnsOHPXyLNcoLtNiXKnvVS1cLDlOzGcMBG0MvGY1ua0An7r2RYX2HdJhbw2 GIgNu/hiG9v/v91RazB9rZvNijAk7QBasf14qsnFQg9hDp6QSXyGQjXFxOkJC1Pr 3UzrtIpEgpZ8Ls+uQtFOT+vZJEBQNNuZ5d7H4vbU2lUj7LajMJw= =176T -----END PGP SIGNATURE----- --2otz2YBkNKpHdJOidjhGzRvIgUzq6EAGT--