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).
