Re: [PATCH v7 02/14] fs: spell out fenced ->i_state accesses with explicit smp_wmb/smp_rmb

Jan Kara
2025-10-10T13:48:51Z

On Thu 09-10-25 09:59:16, Mateusz Guzik wrote:
> The incomming helpers don't ship with _release/_acquire variants, for
> the time being anyway.
>
> Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/fs-writeback.c | 5 +++--
> include/linux/backing-dev.h | 5 +++--
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 2b35e80037fe..9cda19a40ca2 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -476,10 +476,11 @@ static bool inode_do_switch_wbs(struct inode *inode,
> switched = true;
> skip_switch:
> /*
> - * Paired with load_acquire in unlocked_inode_to_wb_begin() and
> + * Paired with an acquire fence in unlocked_inode_to_wb_begin() and
> * ensures that the new wb is visible if they see !I_WB_SWITCH.
> */
> - smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
> + smp_wmb();
> + inode->i_state &= ~I_WB_SWITCH;
>
> xa_unlock_irq(&mapping->i_pages);
> spin_unlock(&inode->i_lock);
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 3e64f14739dd..065cba5dc111 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -277,10 +277,11 @@ unlocked_inode_to_wb_begin(struct inode *inode, struct wb_lock_cookie *cookie)
> rcu_read_lock();
>
> /*
> - * Paired with store_release in inode_switch_wbs_work_fn() and
> + * Paired with a release fence in inode_do_switch_wbs() and
> * ensures that we see the new wb if we see cleared I_WB_SWITCH.
> */
> - cookie->locked = smp_load_acquire(&inode->i_state) & I_WB_SWITCH;
> + cookie->locked = inode->i_state & I_WB_SWITCH;
> + smp_rmb();
>
> if (unlikely(cookie->locked))
> xa_lock_irqsave(&inode->i_mapping->i_pages, cookie->flags);
> --
> 2.34.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR