On Sat 17-02-24 15:23:40, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@xxxxxxxxxx>
>
> Liam and Matthew say that once the RCU read lock is released,
> xa_state is not safe to re-use for the next xas_find() call. But the
> RCU read lock must be released on each loop iteration so that
> dput(), which might_sleep(), can be called safely.
>
> Thus we are forced to walk the offset tree with fresh state for each
> directory entry. xa_find() can do this for us, though it might be a
> little less efficient than maintaining xa_state locally.
>
> We believe that in the current code base, inode->i_rwsem provides
> protection for the xa_state maintained in
> offset_iterate_dir(). However, there is no guarantee that will
> continue to be the case in the future.
>
> Since offset_iterate_dir() doesn't build xa_state locally any more,
> there's no longer a strong need for offset_find_next(). Clean up by
> rolling these two helpers together.
>
> Suggested-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> Message-ID: <170785993027.11135.8830043889278631735.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/libfs.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index eec6031b0155..752e24c669d9 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -402,12 +402,13 @@ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence)
> return vfs_setpos(file, offset, U32_MAX);
> }
>
> -static struct dentry *offset_find_next(struct xa_state *xas)
> +static struct dentry *offset_find_next(struct offset_ctx *octx, loff_t offset)
> {
> struct dentry *child, *found = NULL;
> + XA_STATE(xas, &octx->xa, offset);
>
> rcu_read_lock();
> - child = xas_next_entry(xas, U32_MAX);
> + child = xas_next_entry(&xas, U32_MAX);
> if (!child)
> goto out;
> spin_lock(&child->d_lock);
> @@ -430,12 +431,11 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry)
>
> static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
> {
> - struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode);
> - XA_STATE(xas, &so_ctx->xa, ctx->pos);
> + struct offset_ctx *octx = inode->i_op->get_offset_ctx(inode);
> struct dentry *dentry;
>
> while (true) {
> - dentry = offset_find_next(&xas);
> + dentry = offset_find_next(octx, ctx->pos);
> if (!dentry)
> return ERR_PTR(-ENOENT);
>
> @@ -444,8 +444,8 @@ static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
> break;
> }
>
> + ctx->pos = dentry2offset(dentry) + 1;
> dput(dentry);
> - ctx->pos = xas.xa_index + 1;
> }
> return NULL;
> }
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
