On Wed, 2011-07-27 at 14:40 -0400, Jim Rees wrote:
> From: Peng Tao <bergwolf@xxxxxxxxx>
>
> Save it in layout header instead of in every segment.
>
> Signed-off-by: Peng Tao <peng_tao@xxxxxxx>
> ---
> fs/nfs/pnfs.c | 12 ++++++------
> fs/nfs/pnfs.h | 1 -
> 2 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
> index dae19dd..fbebd2a 100644
> --- a/fs/nfs/pnfs.c
> +++ b/fs/nfs/pnfs.c
> @@ -211,6 +211,7 @@ destroy_layout_hdr(struct pnfs_layout_hdr *lo)
> dprintk("%s: freeing layout cache %p\n", __func__, lo);
> BUG_ON(!list_empty(&lo->plh_layouts));
> NFS_I(lo->plh_inode)->layout = NULL;
> + put_rpccred(lo->plh_lc_cred);
> pnfs_free_layout_hdr(lo);
> }
>
> @@ -1007,6 +1008,10 @@ pnfs_update_layout(struct inode *ino,
> list_del_init(&lo->plh_layouts);
> spin_unlock(&clp->cl_lock);
> }
> + if (first) {
> + lo->plh_lc_cred =
> + get_rpccred(ctx->state->owner->so_cred);
> + }
Hmm... This whole 'first' thing is inherently racy. What if two threads
are calling pnfs_update_layout at the same time: they both see
list_empty(&lo->plh_segs), and both conclude that they need to
initialise the layout header. _BOOM_....
The correct thing to do here is either to initialise the layout header
correctly inside pnfs_find_alloc_layout(), or to add a flag for
->plh_flags that can be used with test_and_clear_bit() to get _one_ of
the processes to perform the initialisation.
Personally, I'd prefer the former.
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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