On Tue, 2021-05-18 at 14:21 -0400, bfields@xxxxxxxxxxxx wrote:
> On Tue, May 18, 2021 at 05:53:47PM +0000, Trond Myklebust wrote:
> > On Sat, 2021-05-15 at 08:02 +0100, Christoph Hellwig wrote:
> > > On Fri, May 14, 2021 at 03:46:57PM +0000, Trond Myklebust wrote:
> > > > Why leave the commit_metadata() call under the lock? If you're
> > > > concerned about latency, then it makes more sense to call
> > > > fh_unlock()
> > > > before flushing those metadata updates to disk.
> > >
> > > Also I'm not sure why the extra inode reference is needed. What
> > > speaks
> > > against just moving the dput out of the locked section?
> >
> > Isn't the inode reference taken just in order to ensure that the
> > call
> > to iput_final() (and in particular the call to
> > truncate_inode_pages_final()) is performed outside the lock?
> >
> > The dput() is presumably usually not particularly expensive, since
> > the
> > dentry is just a completely ordinary negative dentry at this point.
>
> Right, but why bother with the extra ihold/iput instead of just
> postponing the dput?
As I said above, the dentry is negative at this point. It doesn't carry
a reference to the inode any more, so that wouldn't defer the inode
truncation.
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 79b0ff9b151e..aeed93c9874c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4084,7 +4084,6 @@ long do_unlinkat(int dfd, struct filename
> *name)
> inode = dentry->d_inode;
> if (d_is_negative(dentry))
> goto slashes;
> - ihold(inode);
> error = security_path_unlink(&path, dentry);
> if (error)
> goto exit2;
> @@ -4092,11 +4091,10 @@ long do_unlinkat(int dfd, struct filename
> *name)
> error = vfs_unlink(mnt_userns, path.dentry->d_inode,
> dentry,
> &delegated_inode);
> exit2:
> - dput(dentry);
> }
> inode_unlock(path.dentry->d_inode);
> - if (inode)
> - iput(inode); /* truncate the inode here */
> + if (!IS_ERR(dentry))
> + dput(dentry); /* truncate the inode here */
> inode = NULL;
> if (delegated_inode) {
> error = break_deleg_wait(&delegated_inode);
>
> ?
>
> --b.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
