Re: [PATCH 04/16] vfs: do_last(): use inode variable

[Miklos Szeredi]

Nick Piggin <npiggin@xxxxxxxxx> writes:

> On 25 April 2012 22:44, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>> From: Miklos Szeredi <mszeredi@xxxxxxx>
>>
>> Use helper variable instead of path->dentry->d_inode before complete_walk().
>> This will allow this code to be used in RCU mode.
>
> What do you mean, allow it to be used?

I mean allow the code to be shared between RCU and non-RCU mode.  See
10/16.

>
>>
>> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
>> ---
>> Âfs/namei.c | Â Â7 ++++---
>> Â1 files changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/namei.c b/fs/namei.c
>> index 46d4bf6..f21ddb3 100644
>> --- a/fs/namei.c
>> +++ b/fs/namei.c
>> @@ -2360,15 +2360,16 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
>> Â Â Â Âif (error)
>> Â Â Â Â Â Â Â Ând->flags |= LOOKUP_JUMPED;
>>
>> + Â Â Â inode = path->dentry->d_inode ;
>> Â Â Â Âerror = -ENOENT;
>> - Â Â Â if (!path->dentry->d_inode)
>> + Â Â Â if (!inode)
>> Â Â Â Â Â Â Â Âgoto exit_dput;
>>
>> - Â Â Â if (path->dentry->d_inode->i_op->follow_link)
>> + Â Â Â if (inode->i_op->follow_link)
>> Â Â Â Â Â Â Â Âreturn NULL;
>>
>> Â Â Â Âpath_to_nameidata(path, nd);
>> - Â Â Â nd->inode = path->dentry->d_inode;
>> + Â Â Â nd->inode = inode;
>> Â Â Â Â/* Why this, you ask? Â_Now_ we might have grown LOOKUP_JUMPED... */
>> Â Â Â Âerror = complete_walk(nd);
>> Â Â Â Âif (error)
>
> In rcu-walk mode, dentry->d_inode should not be accessed at all,
> outside of the core lookup code that (should) have the correct
> barriers and sequence locks.
>
> That logic should not escape into here, so I'm just not sure what
> you're doing here.

Right, dentry->d_inode is *not* going to be dereferenced in RCU mode.
In RCU mode it will jump to the place just after the "inode =
path->dentry->d_inode;" line.  See patch 10/16.

Thanks,
Miklos
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