[PATCH v2] mm: fix ratelimit_pages update error in dirty_ratio_handler()

[alexjlzheng@gmail.com]

From: Jinliang Zheng <alexjlzheng@tencent.com>

In the dirty_ratio_handler() function, vm_dirty_bytes must be set to
zero before calling writeback_set_ratelimit(), as global_dirty_limits()
always prioritizes the value of vm_dirty_bytes.

That causes ratelimit_pages to still use the value calculated based on
vm_dirty_bytes, which is wrong now.

Fixes: 9d823e8f6b1b ("writeback: per task dirty rate limit")
Signed-off-by: Jinliang Zheng <alexjlzheng@tencent.com>
Reviewed-by: MengEn Sun <mengensun@tencent.com>
Cc: stable@vger.kernel.org
---
Changelog:
v2: A more detailed description
v1: https://lore.kernel.org/linux-fsdevel/20250415083542.6946-1-alexjlzheng@tencent.com/T/#u
---
 mm/page-writeback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c81624bc3969..20e1d76f1eba 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -520,8 +520,8 @@ static int dirty_ratio_handler(const struct ctl_table *table, int write, void *b
 
 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
-		writeback_set_ratelimit();
 		vm_dirty_bytes = 0;
+		writeback_set_ratelimit();
 	}
 	return ret;
 }
-- 
2.49.0