On Thu, Aug 21, 2025 at 04:18:23PM -0400, Josef Bacik wrote:
> Currently, if we are the last iput, and we have the I_DIRTY_TIME bit
> set, we will grab a reference on the inode again and then mark it dirty
> and then redo the put. This is to make sure we delay the time update
> for as long as possible.
>
> We can rework this logic to simply dec i_count if it is not 1, and if it
> is do the time update while still holding the i_count reference.
>
> Then we can replace the atomic_dec_and_lock with locking the ->i_lock
> and doing atomic_dec_and_test, since we did the atomic_add_unless above.
>
> This is preparation for no longer allowing 0 i_count inodes to exist.
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> ---
> fs/inode.c | 31 ++++++++++++++++---------------
> 1 file changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 16acad5583fc..814c03f5dbb1 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1928,22 +1928,23 @@ void iput(struct inode *inode)
> if (!inode)
> return;
> BUG_ON(inode->i_state & I_CLEAR);
> -retry:
> - if (atomic_dec_and_lock(&inode->i_count, &inode->i_lock)) {
> - if (inode->i_nlink && (inode->i_state & I_DIRTY_TIME)) {
> - /*
> - * Increment i_count directly as we still have our
> - * i_obj_count reference still. This is temporary and
> - * will go away in a future patch.
> - */
> - atomic_inc(&inode->i_count);
> - spin_unlock(&inode->i_lock);
> - trace_writeback_lazytime_iput(inode);
> - mark_inode_dirty_sync(inode);
> - goto retry;
> - }
> - iput_final(inode);
> +
> + if (atomic_add_unless(&inode->i_count, -1, 1)) {
> + iobj_put(inode);
> + return;
> }
> +
> + if (inode->i_nlink && (inode->i_state & I_DIRTY_TIME)) {
> + trace_writeback_lazytime_iput(inode);
> + mark_inode_dirty_sync(inode);
> + }
> +
> + spin_lock(&inode->i_lock);
> + if (atomic_dec_and_test(&inode->i_count))
> + iput_final(inode);
Personally, I'd add a
// drops i_lock
comment behind iput_final() but that's a matter of taste tbf.
> + else
> + spin_unlock(&inode->i_lock);
> +
> iobj_put(inode);
> }
> EXPORT_SYMBOL(iput);
This looks a lot less magical than the current variant! We should maybe
split this patch in two. A cleanup patch that removes the questionable
"drop to zero, take lock then increment from zero again" logic and then
in a separate patch add in the iobj_put(). So the cleanup can go to the
front of the series.
