Re: NFS stuck in nfs_lookup_revalidate

[Zdenek Salvet <salvet@ics.muni.cz>]

On Thu, Jun 05, 2025 at 12:00:44AM +0530, Santosh Pradhan wrote:
> I am not sure but I vaguely remember that there was some similar issue and
> Neil introduced store_release_wake_up() which puts a full barrier  smp_mb()
> before calling wake_up_var().
> 
> index d0e0b435a843..e754e3e478a5 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -1830,6 +1830,7 @@ static void unblock_revalidate(struct dentry *dentry)
>  {
>         /* store_release ensures wait_var_event() sees the update */
>         smp_store_release(&dentry->d_fsdata, NULL);
> + smp_mb();
>         wake_up_var(&dentry->d_fsdata);
>  }

Hello,
yes, upon rereading exact definition of smp_store_release(),
I am reasonably sure the comment is wrong and smp_mb() should be used,
it ensures the right ordering between store to d_fsdata and wait queue
data, not the smp_store_release(&dentry->d_fsdata,...).

Best regards,
Zdenek Salvet                                              salvet@ics.muni.cz 
Institute of Computer Science of Masaryk University, Brno, Czech Republic
and CESNET, z.s.p.o., Prague, Czech Republic
Phone: ++420-549 49 6534                           Fax: ++420-541 212 747
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