From: Zqiang <qiang.zhang1211@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: hch@infradead.org, akpm@linux-foundation.org,
sunhao.th@gmail.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Mikulas Patocka <mpatocka@redhat.com>,
Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] mm: backing-dev: use kfree_rcu() instead of synchronize_rcu_expedited()
Date: Mon, 18 Oct 2021 10:15:53 +0800 [thread overview]
Message-ID: <2357d7fe-0679-768e-7319-2f141860af2e@gmail.com> (raw)
In-Reply-To: <YWl1rDO6gCFJE4hp@casper.infradead.org>
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@infradead.org <mailto:willy@infradead.org>>
>>> 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@gmail.com
>>> <mailto:sunhao.th@gmail.com>>
>>> > Signed-off-by: Zqiang <qiang.zhang1211@gmail.com
>>> <mailto: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?
>>>
>>>
>>> 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
next prev parent reply other threads:[~2021-10-18 2:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-14 8:24 [PATCH] mm: backing-dev: use kfree_rcu() instead of synchronize_rcu_expedited() Zqiang
2021-10-14 11:24 ` Matthew Wilcox
2021-10-15 2:57 ` Qiang Zhang
2021-10-15 3:34 ` Qiang Zhang
2021-10-15 5:06 ` Zqiang
2021-10-15 12:35 ` Matthew Wilcox
2021-10-15 13:19 ` Christoph Hellwig
2021-10-18 2:15 ` Zqiang [this message]
2021-10-15 3:39 ` zhangqiang
2021-10-14 12:06 ` Christoph Hellwig
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