Re: NFS/d_splice_alias breakage

Oleg Drokin
2016-06-03T04:58:23Z

On Jun 3, 2016, at 12:26 AM, Al Viro wrote:

> On Thu, Jun 02, 2016 at 11:43:59PM -0400, Oleg Drokin wrote:
>
>>> Which of the call sites had that been and how does one reproduce that fun?
>>> If you feel that posting a reproducer in the open is a bad idea, just send
>>> it off-list...
>>
>> This is fs/nfs/dir.c::nfs_lookup() right after no_entry label.
>
> Bloody hell... Was that sucker hashed on the entry into nfs_lookup()?
> If we get that with call as a method, we are really fucked.
>
> <greps>
>
> Ho-hum... One of the goto no_open; in nfs_atomic_open()? That would
> mean a stale negative dentry in dcache that has escaped revalidation...
> Wait a minute, didn't nfs ->d_revalidate() skip everything in some
> cases, leaving it to ->atomic_open()?
>
> Looks like the right thing to do would be to do d_drop() at no_open:,
> just before we call nfs_lookup(). If not earlier, actually... How
> about the following?

This one cures the insta-crash I was having, and I see no other ill-effects so far.

>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index aaf7bd0..6e3a6f4 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -1536,9 +1536,9 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
> err = PTR_ERR(inode);
> trace_nfs_atomic_open_exit(dir, ctx, open_flags, err);
> put_nfs_open_context(ctx);
> + d_drop(dentry);
> switch (err) {
> case -ENOENT:
> - d_drop(dentry);
> d_add(dentry, NULL);
> nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
> break;