On 2021/10/15 下午8:35, Matthew Wilcox wrote:
On Fri, Oct 15, 2021 at 01:06:02PM +0800, Zqiang wrote:
On 2021/10/15 上午10:57, Qiang Zhang wrote:
Matthew Wilcox <willy@xxxxxxxxxxxxx <mailto:willy@xxxxxxxxxxxxx>>
于2021年10月14日周四 下午7:26写道：
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@xxxxxxxxx
<mailto:sunhao.th@xxxxxxxxx>>
> Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx
<mailto:qiang.zhang1211@xxxxxxxxx>>
> ---
> 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?
Thanks for your advice, I find this bdi_tree is traversed under the
protection of a spin lock, not under the protection of RCU.
I find this modification does not avoid the problem described in patch,
the flush_delayed_work() may be called in release_bdi()
The same will cause problems.
may be we can replace queue_rcu_work() of call_rcu(&inode->i_rcu,
i_callback) or do you have any better suggestions?
What? All I was suggesting was:
+++ b/include/linux/backing-dev-defs.h
@@ -168,7 +168,10 @@ struct bdi_writeback {
struct backing_dev_info {
u64 id;
- struct rb_node rb_node; /* keyed by ->id */
+ union {
+ struct rb_node rb_node; /* keyed by ->id */
+ struct rcu_head rcu;
+ };
struct list_head bdi_list;
unsigned long ra_pages; /* max readahead in PAGE_SIZE units */
unsigned long io_pages; /* max allowed IO size */
Christoph, independent of the inode lifetime problem, this actually seems
like a good approach to take. I don't see why we should synchronize_rcu()
here? Adding Jens (original introducer of the synchronize_rcu()), Mikulas
(converted it to use _expedited) and Tejun (worked around a problem when
using _expedited).
Sorry，this my mistake. this problem and the inode lifetime cycle are
two different problems
Can this modification which use kfree_rcu() instead of synchronize_rcu()
be accepted?
Thanks
Zqiang
