On Tue, 13 Aug 2013, Yan, Zheng wrote:
> From: "Yan, Zheng" <zheng.z.yan@xxxxxxxxx>
>
> The d_prune dentry operation is used to notify filesystem when VFS
> about to prune a hashed dentry from the dcache. There are three
> code paths that prune dentries: shrink_dcache_for_umount_subtree(),
> prune_dcache_sb() and d_prune_aliases(). For the d_prune_aliases()
> case, VFS unhashes the dentry first, then call the d_prune dentry
> operation. This confuses ceph_d_prune() (ceph uses the d_prune
> dentry operation to maintain a flag indicating whether the complete
> contents of a directory are in the dcache, pruning unhashed dentry
> does not affect dir's completeness)
>
> This patch fixes the issue by calling the d_prune dentry operation
> in d_prune_aliases(), before unhashing the dentry. Also make VFS
> only call the d_prune dentry operation for hashed dentry, to avoid
> calling the d_prune dentry operation twice when dentry is pruned
> by d_prune_aliases().
>
> Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
Reviewed-by: Sage Weil <sage@xxxxxxxxxxx>
This is behaving well under my testing, seems to resolve the race we were
encoutering before, and cleans up the d_prune semantics nicely IMO.
Al, does this look okay to you?
Thanks!
sage
> ---
> fs/dcache.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 87bdb53..612e99b 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -472,7 +472,7 @@ relock:
> * inform the fs via d_prune that this dentry is about to be
> * unhashed and destroyed.
> */
> - if (dentry->d_flags & DCACHE_OP_PRUNE)
> + if ((dentry->d_flags & DCACHE_OP_PRUNE) && !d_unhashed(dentry))
> dentry->d_op->d_prune(dentry);
>
> dentry_lru_del(dentry);
> @@ -719,6 +719,14 @@ restart:
> hlist_for_each_entry(dentry, &inode->i_dentry, d_alias) {
> spin_lock(&dentry->d_lock);
> if (!dentry->d_count) {
> + /*
> + * inform the fs via d_prune that this dentry
> + * is about to be unhashed and destroyed.
> + */
> + if ((dentry->d_flags & DCACHE_OP_PRUNE) &&
> + !d_unhashed(dentry))
> + dentry->d_op->d_prune(dentry);
> +
> __dget_dlock(dentry);
> __d_drop(dentry);
> spin_unlock(&dentry->d_lock);
> @@ -907,7 +915,8 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
> * inform the fs that this dentry is about to be
> * unhashed and destroyed.
> */
> - if (dentry->d_flags & DCACHE_OP_PRUNE)
> + if ((dentry->d_flags & DCACHE_OP_PRUNE) &&
> + !d_unhashed(dentry))
> dentry->d_op->d_prune(dentry);
>
> dentry_lru_del(dentry);
> --
> 1.8.1.4
>
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