linux-kernel - Re: [RFC][PATCH 07/10] orangefs: Use RCU for destroy

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Date:   Sat, 25 Feb 2017 15:31:14 -0500
From:   Mike Marshall <hubcap@...ibond.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chris Mason <clm@...com>, LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>, elena.reshetova@...el.com,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC][PATCH 07/10] orangefs: Use RCU for destroy_inode

After looking through the code and seeing how some other filesystems
use call_rcu, it seems that call_rcu has to do with consistency and
waiting for stuff to complete before returning an object to the slab cache,
whereas we were just calling kmem_cache_free without worrying about that
kind of stuff...

Is that a "close enough" description of the error that is being
fixed here?

-Mike

On Fri, Feb 24, 2017 at 6:00 PM, Mike Marshall <hubcap@...ibond.com> wrote:
> Thanks Al... I was going to try and evaluate that patch next
> week, now all I have to do is test it <g> ...
>
> -Mike
>
> On Fri, Feb 24, 2017 at 3:52 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>> That, AFAICS, fixes a real bug.  Applied, and it needs Cc:stable as well.
>>
>>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>> ---
>>>  fs/orangefs/super.c |    9 ++++++++-
>>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> --- a/fs/orangefs/super.c
>>> +++ b/fs/orangefs/super.c
>>> @@ -115,6 +115,13 @@ static struct inode *orangefs_alloc_inod
>>>       return &orangefs_inode->vfs_inode;
>>>  }
>>>
>>> +static void orangefs_i_callback(struct rcu_head *head)
>>> +{
>>> +     struct inode *inode = container_of(head, struct inode, i_rcu);
>>> +     struct orangefs_inode_s *orangefs_inode = ORANGEFS_I(inode);
>>> +     kmem_cache_free(orangefs_inode_cache, orangefs_inode);
>>> +}
>>> +
>>>  static void orangefs_destroy_inode(struct inode *inode)
>>>  {
>>>       struct orangefs_inode_s *orangefs_inode = ORANGEFS_I(inode);
>>> @@ -123,7 +130,7 @@ static void orangefs_destroy_inode(struc
>>>                       "%s: deallocated %p destroying inode %pU\n",
>>>                       __func__, orangefs_inode, get_khandle_from_ino(inode));
>>>
>>> -     kmem_cache_free(orangefs_inode_cache, orangefs_inode);
>>> +     call_rcu(&inode->i_rcu, orangefs_i_callback);
>>>  }
>>>
>>>  /*
>>>
>>>