linux-kernel - Re: [RFC PATCH 1/2] autofs: set compat flag on sbi when daemon uses 32bit addressation

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Message-ID: <a5488db7-e42a-753c-08ba-008579c1ecd6@themaw.net>
Date:   Thu, 14 Sep 2017 19:29:08 +0800
From:   Ian Kent <raven@...maw.net>
To:     skinsbursky@...tuozzo.com
Cc:     autofs@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...nvz.org, ldv@...linux.org
Subject: Re: [RFC PATCH 1/2] autofs: set compat flag on sbi when daemon uses
 32bit addressation

On 14/09/17 17:24, Stanislav Kinsburskiy wrote:
> 
> 
> 14.09.2017 02:38, Ian Kent пишет:
>> On 01/09/17 19:21, Stanislav Kinsburskiy wrote:
>>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>
>>> ---
>>>  fs/autofs4/autofs_i.h  |    3 +++
>>>  fs/autofs4/dev-ioctl.c |    3 +++
>>>  fs/autofs4/inode.c     |    4 +++-
>>>  3 files changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
>>> index 4737615..3da105f 100644
>>> --- a/fs/autofs4/autofs_i.h
>>> +++ b/fs/autofs4/autofs_i.h
>>> @@ -120,6 +120,9 @@ struct autofs_sb_info {
>>>  	struct list_head active_list;
>>>  	struct list_head expiring_list;
>>>  	struct rcu_head rcu;
>>> +#ifdef CONFIG_COMPAT
>>> +	unsigned is32bit:1;
>>> +#endif
>>>  };
>>>  
>>>  static inline struct autofs_sb_info *autofs4_sbi(struct super_block *sb)
>>> diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
>>> index b7c816f..467d6c4 100644
>>> --- a/fs/autofs4/dev-ioctl.c
>>> +++ b/fs/autofs4/dev-ioctl.c
>>> @@ -397,6 +397,9 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
>>>  		sbi->pipefd = pipefd;
>>>  		sbi->pipe = pipe;
>>>  		sbi->catatonic = 0;
>>> +#ifdef CONFIG_COMPAT
>>> +		sbi->is32bit = is_compat_task();
>>> +#endif
>>>  	}
>>>  out:
>>>  	put_pid(new_pid);
>>> diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
>>> index 09e7d68..21d3c0b 100644
>>> --- a/fs/autofs4/inode.c
>>> +++ b/fs/autofs4/inode.c
>>> @@ -301,7 +301,9 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
>>>  	} else {
>>>  		sbi->oz_pgrp = get_task_pid(current, PIDTYPE_PGID);
>>>  	}
>>> -
>>> +#ifdef CONFIG_COMPAT
>>> +	sbi->is32bit = is_compat_task();
>>> +#endif
>>>  	if (autofs_type_trigger(sbi->type))
>>>  		__managed_dentry_set_managed(root);
>>>  
>>>
>>
>> Not sure about this.
>>
>> Don't you think it would be better to avoid the in code #ifdefs by doing some
>> checks and defines in the header file and defining what's need to just use
>> is_compat_task().
>>
> 
> Yes, might be...
> 
>> Not sure 2 patches are needed for this either ......
>>
> 
> Well, I found this issue occasionally.

I'm wondering what the symptoms are?

> And, frankly speaking, it's not clear to me, whether this issue is important at all, so I wanted to clarify this first.
> Thanks to O_DIRECT, the only way to catch the issue is to try to read more, than expected, in compat task (that's how I found it).

Right, the O_DIRECT patch from Linus was expected to fix the structure
alignment problem. The stuct field offsets are ok aren't they?

> I don't see any other flaw so far. And if so, that, probably, we shouldn't care about the issue at all.
> What do you think?

If we are seeing hangs, incorrect struct fields or similar something
should be done about it but if all is actually working ok then the
O_DIRECT fix is doing it's job and further changes aren't necessary.

Ian