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 [EMAIL PROTECTED] http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am!
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