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SubjectRe: [PATCH] mm: backing-dev: use kfree_rcu() instead of synchronize_rcu_expedited()
On Thu, Oct 14, 2021 at 04:24:33PM +0800, Zqiang wrote:
> The bdi_remove_from_list() is called in RCU softirq, however the
> synchronize_rcu_expedited() will produce sleep action, use kfree_rcu()
> instead of it.
>
> Reported-by: Hao Sun <sunhao.th@gmail.com>
> Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
> ---
> include/linux/backing-dev-defs.h | 1 +
> mm/backing-dev.c | 4 +---
> 2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
> index 33207004cfde..35a093384518 100644
> --- a/include/linux/backing-dev-defs.h
> +++ b/include/linux/backing-dev-defs.h
> @@ -202,6 +202,7 @@ struct backing_dev_info {
> #ifdef CONFIG_DEBUG_FS
> struct dentry *debug_dir;
> #endif
> + struct rcu_head rcu;
> };

Instead of growing struct backing_dev_info, it seems to me this rcu_head
could be placed in a union with rb_node, since it will have been removed
from the bdi_tree by this point and the tree is never walked under
RCU protection?

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