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

Mateusz Guzik
2025-10-09T07:59:44Z

The incomming helpers don't ship with _release/_acquire variants, for
the time being anyway.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
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