From: Chuck Lever chuck.lever@oracle.com
[ Upstream commit 3f6d810665dfde0d33785420618ceb03fba0619d ]
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@Oracle.com Message-ID: 170785993027.11135.8830043889278631735.stgit@91.116.238.104.host.secureserver.net Signed-off-by: Chuck Lever chuck.lever@oracle.com Link: https://lore.kernel.org/r/170820142021.6328.15047865406275957018.stgit@91.11... Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Chuck Lever chuck.lever@oracle.com --- fs/libfs.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/fs/libfs.c b/fs/libfs.c index dc0f7519045f..430f7c95336c 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -401,12 +401,13 @@ 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); @@ -429,12 +430,11 @@ 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);
@@ -443,8 +443,8 @@ 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; }