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? -Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
