Date: Fri, 5 Oct 2007 09:32:02 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Jeff Roberson <jroberson@chesapeake.net> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org, John Baldwin <jhb@FreeBSD.org> Subject: Re: cvs commit: src/sys/fs/devfs devfs_vnops.c src/sys/fs/fifofs fifo_vnops.c src/sys/kern uipc_usrreq.c vfs_vnops.c src/sys/vm vnode_pager.c Message-ID: <20071005073202.GA94586@garage.freebsd.pl> In-Reply-To: <20071004182759.U912@10.0.0.1> References: <200710032106.l93L65bv095725@repoman.freebsd.org> <20071003164642.B615@10.0.0.1> <200710041219.13202.jhb@freebsd.org> <20071004182759.U912@10.0.0.1>
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[-- Attachment #1 --] On Thu, Oct 04, 2007 at 06:29:25PM -0700, Jeff Roberson wrote: > On Thu, 4 Oct 2007, John Baldwin wrote: > > >On Wednesday 03 October 2007 07:48:00 pm Jeff Roberson wrote: > >>On Wed, 3 Oct 2007, John Baldwin wrote: > >> > >>>jhb 2007-10-03 21:06:05 UTC > >>> > >>> FreeBSD src repository > >>> > >>> Modified files: (Branch: RELENG_6) > >>> sys/fs/devfs devfs_vnops.c > >>> sys/fs/fifofs fifo_vnops.c > >>> sys/kern uipc_usrreq.c vfs_vnops.c > >>> sys/vm vnode_pager.c > >>> Log: > >>> MFC: Always use an exclusive lock on the leaf vnode during an open() > >>> when > >>> shared lookups are enabled. This closes a few races including a race > >where > >>> concurrent opens of a fifo could result in different v_fifoinfo > >structures > >>> in different threads. > >> > >>Long term we should really look for a better solution to this problem. > >>There are a number of was to improve snapshots in ffs by fixing shared > >>locking. > > > >I don't disagree. The fifo case can be fixed easily enough in the fifo > >code > >by using fifo_mtx to protect v_fifoinfo perhaps (or doing an upgrade on the > >vnode lock?), but for the MFC I didn't want to have to fix each of the > >races > >with open(2). Probably better to fix it more properly in HEAD first. > > Definitely someting for head. Were there any others that you ran into > besides v_fifoinfo? We should audit this more closely anyhow. I have > been reluctant to push too much shared locking into VFS because it's not > been so carefully studied. You probably talking about my patch. I agree, but there are many inconsistencies. People tend to use exclusive locking everywhere. We could start from converting places where sometimes we use shared locking and sometimes exclusive, eg. VOP_READ(), VOP_GETATTR(), etc. -- Pawel Jakub Dawidek http://www.wheel.pl pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQFHBehyForvXbEpPzQRAi/UAKDZ8XfXJoG2A5iDl7tGaNCsnqKkWACgwez7 E6TTVa+ymrZg74FHnX7DBCk= =dh7V -----END PGP SIGNATURE-----help
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