On Thu, Mar 8, 2018 at 2:33 PM, David Sterba <dsterba@xxxxxxxx> wrote:
> The allocation of tree_mod_elem can be delayed after tree_mod_dont_log.
> In case it causes the function to return, the allocation would be
> redundant. Otherwise it could cause unnecessary failure if there's not
> enough memory.
Nop, the allocation must be made before calling tree_mod_dont_log(),
as that function acquires a write lock.
That's why there's a call to tree_mod_need_log() before the allocation
and a call to tree_mod_dont_log() after (they do the same checks).
>
> Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> ---
> fs/btrfs/ctree.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 30950439731e..da6e2c3ca2d0 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -521,15 +521,13 @@ static noinline int tree_mod_log_insert_key(struct extent_buffer *eb, int slot,
> if (!tree_mod_need_log(eb->fs_info, eb))
> return 0;
>
> + if (tree_mod_dont_log(eb->fs_info, eb))
> + return 0;
> +
> tm = alloc_tree_mod_elem(eb, slot, op, flags);
> if (!tm)
> return -ENOMEM;
>
> - if (tree_mod_dont_log(eb->fs_info, eb)) {
> - kfree(tm);
> - return 0;
> - }
> -
> ret = __tree_mod_log_insert(eb->fs_info, tm);
> write_unlock(&eb->fs_info->tree_mod_log_lock);
> if (ret)
> --
> 2.16.2
>
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Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
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