Re: [PATCH] VFS: call synchronize_rcu after kill_sb.

[Tao Ma <tm@tao.ma>]

On 02/09/2011 01:25 AM, Boaz Harrosh wrote:
> On 02/08/2011 06:57 PM, Aneesh Kumar K. V wrote:
>    
>> On Mon, 07 Feb 2011 15:14:40 +0200, Boaz Harrosh<bharrosh@panasas.com>  wrote:
>>      
>>> On 02/05/2011 11:01 AM, Tao Ma wrote:
>>>        
>>>> From: Tao Ma<boyu.mt@taobao.com>
>>>>
>>>> In fa0d7e3, we use rcu free inode instead of freeing the inode
>>>> directly. It causes a problem when we rmmod immediately after
>>>> we umount the volume[1].
>>>>
>>>> So we need to call synchronize_rcu after we kill_sb so that
>>>> the inode is freed before we do rmmod. The idea is inspired
>>>> by Chris Mason[2]. I tested with ext4 by umount+rmmod and it
>>>> doesn't show any error by now.
>>>>
>>>> 1. http://marc.info/?l=linux-fsdevel&m=129680863330185&w=2
>>>> 2. http://marc.info/?l=linux-fsdevel&m=129684698713709&w=2
>>>>
>>>> Cc: Nick Piggin<npiggin@kernel.dk>
>>>> Cc: Al Viro<viro@zeniv.linux.org.uk>
>>>> Cc: Chris Mason<chris.mason@oracle.com>
>>>> Cc: Boaz Harrosh<bharrosh@panasas.com>
>>>> Signed-off-by: Tao Ma<boyu.mt@taobao.com>
>>>> ---
>>>>   fs/super.c |    7 +++++++
>>>>   1 files changed, 7 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/fs/super.c b/fs/super.c
>>>> index 74e149e..315bce9 100644
>>>> --- a/fs/super.c
>>>> +++ b/fs/super.c
>>>> @@ -177,6 +177,13 @@ void deactivate_locked_super(struct super_block *s)
>>>>   	struct file_system_type *fs = s->s_type;
>>>>   	if (atomic_dec_and_test(&s->s_active)) {
>>>>   		fs->kill_sb(s);
>>>> +		/*
>>>> +		 * We need to synchronize rcu here so that
>>>> +		 * the delayed rcu inode free can be executed
>>>> +		 * before we put_super.
>>>> +		 * https://bugzilla.kernel.org/show_bug.cgi?id=27652
>>>> +		 */
>>>> +		synchronize_rcu();
>>>>   		put_filesystem(fs);
>>>>   		put_super(s);
>>>>   	} else {
>>>>          
>>>
>>>        
> <>
>    
>> http://lwn.net/Articles/217484/ explains how to wait for rcu callback to finish
>>
>> -aneesh
>>      
> Yes thanks Aneesh, rcu_barrier does the trick
> ---
> From: Boaz Harrosh<bharrosh@panasas.com>
>
> In fa0d7e3, we use rcu free inode instead of freeing the inode
> directly. It causes a problem when we rmmod immediately after
> we umount the volume[1].
>
> So we need to call rcu_barrier after we kill_sb so that
> the inode is freed before we do rmmod. The idea is inspired
> by Aneesh Kumar. rcu_barrier will wait for all callbacks
> to end before preceding. The original patch was done by
> Tao Ma, but synchronize_rcu() is not enough here.
>
> 1. http://marc.info/?l=linux-fsdevel&m=129680863330185&w=2
> 2. http://marc.info/?l=linux-fsdevel&m=129684698713709&w=2
>
> Cc: Nick Piggin<npiggin@kernel.dk>
> Cc: Al Viro<viro@zeniv.linux.org.uk>
> Cc: Chris Mason<chris.mason@oracle.com>
> Cc: Tao Ma<boyu.mt@taobao.com>
> Signed-off-by: Boaz Harrosh<bharrosh@panasas.com>
>    
It works now in my ext4 test box. Thanks for your work.
Tested-by: Tao Ma <boyu.mt@taobao.com>
> ---
> git diff --stat -p -M fs/super.c
>   fs/super.c |    1 +
>   1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/fs/super.c b/fs/super.c
> index 74e149e..5fd4ec9 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -177,6 +177,13 @@ void deactivate_locked_super(struct super_block *s)
>   	struct file_system_type *fs = s->s_type;
>   	if (atomic_dec_and_test(&s->s_active)) {
>   		fs->kill_sb(s);
> +		/*
> +		 * We need to synchronize rcu here so that
> +		 * the delayed rcu inode free can be executed
> +		 * before we put_super.
> +		 * https://bugzilla.kernel.org/show_bug.cgi?id=27652
> +		 */
> +		rcu_barrier();
>   		put_filesystem(fs);
>   		put_super(s);
>   	} else {
> --
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