From owner-svn-src-all@FreeBSD.ORG Tue Sep 7 08:04:51 2010 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B99A810656C1; Tue, 7 Sep 2010 08:04:51 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mail.zoral.com.ua (mx0.zoral.com.ua [91.193.166.200]) by mx1.freebsd.org (Postfix) with ESMTP id 4CF718FC14; Tue, 7 Sep 2010 08:04:50 +0000 (UTC) Received: from deviant.kiev.zoral.com.ua (root@deviant.kiev.zoral.com.ua [10.1.1.148]) by mail.zoral.com.ua (8.14.2/8.14.2) with ESMTP id o8784lB6028571 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 7 Sep 2010 11:04:47 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (kostik@localhost [127.0.0.1]) by deviant.kiev.zoral.com.ua (8.14.4/8.14.4) with ESMTP id o8784kLb003055; Tue, 7 Sep 2010 11:04:46 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by deviant.kiev.zoral.com.ua (8.14.4/8.14.4/Submit) id o8784kvL003054; Tue, 7 Sep 2010 11:04:46 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: deviant.kiev.zoral.com.ua: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 7 Sep 2010 11:04:46 +0300 From: Kostik Belousov To: Ryan Stone Message-ID: <20100907080446.GA2853@deviant.kiev.zoral.com.ua> References: <201009070023.o870Njtg072607@svn.freebsd.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="5mCyUwZo2JvN/JJP" Content-Disposition: inline In-Reply-To: <201009070023.o870Njtg072607@svn.freebsd.org> User-Agent: Mutt/1.4.2.3i X-Virus-Scanned: clamav-milter 0.95.2 at skuns.kiev.zoral.com.ua X-Virus-Status: Clean X-Spam-Status: No, score=-2.2 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_50, DNS_FROM_OPENWHOIS autolearn=no version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on skuns.kiev.zoral.com.ua Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r212281 - head/sys/vm X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 07 Sep 2010 08:04:51 -0000 --5mCyUwZo2JvN/JJP Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Sep 07, 2010 at 12:23:45AM +0000, Ryan Stone wrote: > Author: rstone > Date: Tue Sep 7 00:23:45 2010 > New Revision: 212281 > URL: http://svn.freebsd.org/changeset/base/212281 >=20 > Log: > In munmap() downgrade the vm_map_lock to a read lock before taking a re= ad > lock on the pmc-sx lock. This prevents a deadlock with > pmc_log_process_mappings, which has an exclusive lock on pmc-sx and tri= es > to get a read lock on a vm_map. Downgrading the vm_map_lock in munmap > allows pmc_log_process_mappings to continue, preventing the deadlock. > =20 > Without this change I could cause a deadlock on a multicore 8.1-RELEASE > system by having one thread constantly mmap'ing and then munmap'ing a > PROT_EXEC mapping in a loop while I repeatedly invoked and stopped pmcs= tat > in system-wide sampling mode. > =20 > Reviewed by: fabient > Approved by: emaste (mentor) > MFC after: 2 weeks >=20 > Modified: > head/sys/vm/vm_mmap.c >=20 > Modified: head/sys/vm/vm_mmap.c > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D > --- head/sys/vm/vm_mmap.c Mon Sep 6 23:52:04 2010 (r212280) > +++ head/sys/vm/vm_mmap.c Tue Sep 7 00:23:45 2010 (r212281) > @@ -579,6 +579,7 @@ munmap(td, uap) > * Inform hwpmc if the address range being unmapped contains > * an executable region. > */ > + pkm.pm_address =3D (uintptr_t) NULL; > if (vm_map_lookup_entry(map, addr, &entry)) { > for (; > entry !=3D &map->header && entry->start < addr + size; > @@ -587,16 +588,23 @@ munmap(td, uap) > entry->end, VM_PROT_EXECUTE) =3D=3D TRUE) { > pkm.pm_address =3D (uintptr_t) addr; > pkm.pm_size =3D (size_t) size; > - PMC_CALL_HOOK(td, PMC_FN_MUNMAP, > - (void *) &pkm); > break; > } > } > } > #endif > - /* returns nothing but KERN_SUCCESS anyway */ > vm_map_delete(map, addr, addr + size); > + > +#ifdef HWPMC_HOOKS > + /* downgrade the lock to prevent a LOR with the pmc-sx lock */ > + vm_map_lock_downgrade(map); > + if (pkm.pm_address !=3D (uintptr) NULL) > + PMC_CALL_HOOK(td, PMC_FN_MUNMAP, (void *) &pkm); > + vm_map_unlock_read(map); > +#else > vm_map_unlock(map); > +#endif > + /* vm_map_delete returns nothing but KERN_SUCCESS anyway */ > return (0); > } > =20 Note that vm_map_unlock() is more then just dropping the lock on the map. Due to ordering of the vnode lock before vm map lock, vm_map_unlock() processes the deferred free entries after map lock is dropped. After your change, the deferred list might keep entries for some time until next unlock is performed. I think the two changes could be done: - only perform downgrade when hook is indeed going to be called; - before vm_map_unlock_read, check for deferred_freelist being not NULL, and if so, do vm_map_lock()/vm_map_unlock() after unlock_read. --5mCyUwZo2JvN/JJP Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD) iEYEARECAAYFAkyF8h4ACgkQC3+MBN1Mb4ifPgCeJ7DecLEIMBMWNZLqwDHMBOBg ip8AoLFiD46h+Q3vTMegW2GEkh20wT+V =9IsU -----END PGP SIGNATURE----- --5mCyUwZo2JvN/JJP--