On Fri, Jan 09, 2015 at 10:23:28AM +1100, Dave Chinner wrote: > On Thu, Jan 08, 2015 at 10:32:05AM -0500, Brian Foster wrote: > > On Thu, Jan 08, 2015 at 08:52:56AM +1100, Dave Chinner wrote: > > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > > > Al Viro noticed a generic set of issues to do with filehandle lookup > > > racing with dentry cache setup. They involve a filehandle lookup > > > occurring while an inode is being created and the filehandle lookup > > > racing with the dentry creation for the real file. This can lead to > > > multiple dentries for the one path being instantiated. There are a > > > host of other issues around this same set of paths. > > > > > > The underlying cause is that file handle lookup only waits on inode > > > cache instantiation rather than full dentry cache instantiation. XFS > > > is mostly immune to the problems discovered due to it's own internal > > > inode cache, but there are a couple of corner cases where races can > > > happen. > > > > > > We currently clear the XFS_INEW flag when the inode is fully set up > > > after insertion into the cache. Newly allocated inodes are inserted > > > locked and so aren't usable until the allocation transaction > > > commits. This, however, occurs before the dentry and security > > > information is fully initialised and hence the inode is unlocked and > > > available for lookups to find too early. > > > > > > To solve the problem, only clear the XFS_INEW flag for newly created > > > inodes once the dentry is fully instantiated. This means lookups > > > will retry until the XFS_INEW flag is removed from the inode and > > > hence avoids the race conditions in questions. > > > > > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > .... > > > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c > > > index ce80eeb..8be5bb5 100644 > > > --- a/fs/xfs/xfs_iops.c > > > +++ b/fs/xfs/xfs_iops.c > > > @@ -186,6 +186,8 @@ xfs_generic_create( > > > else > > > d_instantiate(dentry, inode); > > > > > > + xfs_finish_inode_setup(ip); > > > + > > > out_free_acl: > > > if (default_acl) > > > posix_acl_release(default_acl); > > > @@ -194,6 +196,7 @@ xfs_generic_create( > > > return error; > > > > > > out_cleanup_inode: > > > + xfs_finish_inode_setup(ip); > > > if (!tmpfile) > > > xfs_cleanup_inode(dir, inode, dentry); > > > iput(inode); > > > @@ -366,9 +369,11 @@ xfs_vn_symlink( > > > goto out_cleanup_inode; > > > > > > d_instantiate(dentry, inode); > > > + xfs_finish_inode_setup(cip); > > > return 0; > > > > > > out_cleanup_inode: > > > + xfs_finish_inode_setup(cip); > > > xfs_cleanup_inode(dir, inode, dentry); > > > iput(inode); > > > out: > > > > Ok, but what about post-inode-allocation failure conditions down in > > xfs_create()? I don't know if there's any real harm in releasing an > > I_NEW inode, but iput_final() does throw a warning. Same general > > question applies to xfs_create_tmpfile(), etc.. > > Ah, good point, I missed those. > > Where/how are you getting warnings thrown? I'm not seeing anything > from xfstests runs? > Oh, I hadn't reproduced warnings as such. I was just digging down that path and came across this in iput_final(): WARN_ON(inode->i_state & I_NEW); Brian > -Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
