From: Imran Khan <imran.f.khan@oracle.com>
To: Ian Kent <raven@themaw.net>, Anders Roxell <anders.roxell@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Tejun Heo <tj@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Minchan Kim <minchan@kernel.org>,
Eric Sandeen <sandeen@sandeen.net>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Rick Lindsley <ricklind@linux.vnet.ibm.com>,
David Howells <dhowells@redhat.com>,
Miklos Szeredi <miklos@szeredi.hu>,
Carlos Maiolino <cmaiolino@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Kernel Mailing List <linux-kernel@vger.kernel.org>,
elver@google.com
Subject: Re: [PATCH 1/2] kernfs: dont take i_lock on inode attr read
Date: Thu, 27 Jul 2023 15:35:58 +1000 [thread overview]
Message-ID: <8b0a1619-1e39-fc3a-1226-f3b167e64646@oracle.com> (raw)
In-Reply-To: <3505769d-9e7a-e76d-3aa7-286d689345b6@oracle.com>
Hello again Ian,
I take back my previous comment :).
On 27/7/2023 2:30 pm, Imran Khan wrote:
> Hello Ian,
> Sorry for late reply. I was about to reply this week.
>
> On 27/7/2023 10:38 am, Ian Kent wrote:
>> On 20/7/23 10:03, Ian Kent wrote:
>>> On Wed, 2023-07-19 at 12:23 +0800, Ian Kent wrote:
>
> [...]
>>> I do see a problem with recent changes.
>>>
>>> I'll send this off to Greg after I've done some testing (primarily just
>>> compile and function).
>>>
>>> Here's a patch which describes what I found.
>>>
>>> Comments are, of course, welcome, ;)
>>
>> Anders I was hoping you would check if/what lockdep trace
>>
>> you get with this patch.
>>
>>
>> Imran, I was hoping you would comment on my change as it
>>
>> relates to the kernfs_iattr_rwsem changes.
>>
>>
>> Ian
>>
>>>
>>> kernfs: fix missing kernfs_iattr_rwsem locking
>>>
>>> From: Ian Kent <raven@themaw.net>
>>>
>>> When the kernfs_iattr_rwsem was introduced a case was missed.
>>>
>>> The update of the kernfs directory node child count was also protected
>>> by the kernfs_rwsem and needs to be included in the change so that the
>>> child count (and so the inode n_link attribute) does not change while
>>> holding the rwsem for read.
>>>
>
> kernfs direcytory node's child count changes in kernfs_(un)link_sibling and
> these are getting invoked while adding (kernfs_add_one),
> removing(__kernfs_remove) or moving (kernfs_rename_ns)a node. Each of these
> operations proceed under kernfs_rwsem and I see each invocation of
> kernfs_link/unlink_sibling during the above mentioned operations is happening
> under kernfs_rwsem.
> So the child count should still be protected by kernfs_rwsem and we should not
> need to acquire kernfs_iattr_rwsem in kernfs_link/unlink_sibling.
>
kernfs_refresh_inode can still race against kernfs_link/unlink_siblings. So your
change looks good to me.
My tests are not showing any issues either. ( I tested on 4.14 and 5.4 kernels
as well).
Fee free to add my RB.
Reviewed-by: Imran Khan <imran.f.khan@oracle.com>
> Kindly let me know your thoughts. I would still like to see new lockdep traces
> with this change.
>
> Thanks,
> Imran
>
>>> Fixes: 9caf696142 (kernfs: Introduce separate rwsem to protect inode
>>> attributes)
>>>
>>> Signed-off-by: Ian Kent <raven@themaw.net>
>>> Cc: Anders Roxell <anders.roxell@linaro.org>
>>> Cc: Imran Khan <imran.f.khan@oracle.com>
>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>> Cc: Minchan Kim <minchan@kernel.org>
>>> Cc: Eric Sandeen <sandeen@sandeen.net>
>>> ---
>>> fs/kernfs/dir.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
>>> index 45b6919903e6..6e84bb69602e 100644
>>> --- a/fs/kernfs/dir.c
>>> +++ b/fs/kernfs/dir.c
>>> @@ -383,9 +383,11 @@ static int kernfs_link_sibling(struct kernfs_node
>>> *kn)
>>> rb_insert_color(&kn->rb, &kn->parent->dir.children);
>>> /* successfully added, account subdir number */
>>> + down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
>>> if (kernfs_type(kn) == KERNFS_DIR)
>>> kn->parent->dir.subdirs++;
>>> kernfs_inc_rev(kn->parent);
>>> + up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
>>> return 0;
>>> }
>>> @@ -408,9 +410,11 @@ static bool kernfs_unlink_sibling(struct
>>> kernfs_node *kn)
>>> if (RB_EMPTY_NODE(&kn->rb))
>>> return false;
>>> + down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
>>> if (kernfs_type(kn) == KERNFS_DIR)
>>> kn->parent->dir.subdirs--;
>>> kernfs_inc_rev(kn->parent);
>>> + up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
>>> rb_erase(&kn->rb, &kn->parent->dir.children);
>>> RB_CLEAR_NODE(&kn->rb);
>>>
next prev parent reply other threads:[~2023-07-27 5:38 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-18 2:32 [PATCH 0/2] kernfs: remove i_lock usage that isn't needed Ian Kent
2022-10-18 2:32 ` [PATCH 1/2] kernfs: dont take i_lock on inode attr read Ian Kent
2022-10-24 8:50 ` Miklos Szeredi
2022-10-31 22:30 ` Tejun Heo
2022-12-21 13:34 ` Anders Roxell
2022-12-22 23:11 ` Ian Kent
2022-12-29 9:20 ` Arnd Bergmann
2022-12-29 13:07 ` Ian Kent
2023-01-23 3:11 ` Ian Kent
2023-07-18 19:00 ` Anders Roxell
2023-07-19 4:23 ` Ian Kent
2023-07-20 2:03 ` Ian Kent
2023-07-26 13:49 ` Miklos Szeredi
2023-07-27 0:38 ` Ian Kent
2023-07-27 4:30 ` Imran Khan
2023-07-27 5:35 ` Imran Khan [this message]
2023-07-28 0:00 ` Ian Kent
2023-07-28 0:16 ` Ian Kent
2023-07-28 1:06 ` Imran Khan
2023-07-28 1:29 ` Ian Kent
2022-10-18 2:32 ` [PATCH 2/2] kernfs: dont take i_lock on revalidate Ian Kent
2022-10-24 8:38 ` Miklos Szeredi
2022-10-31 22:31 ` Tejun Heo
2022-11-01 7:46 ` Amir Goldstein
2022-11-01 8:09 ` Ian Kent
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