linux-kernel - Re: [PATCH] fs: record task name which froze superblock

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Date:	Wed, 18 Feb 2015 10:18:12 +0000
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	Jan Kara <jack@...e.cz>, Alexey Dobriyan <adobriyan@...il.com>
CC:	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	cluster-devel@...hat.com
Subject: Re: [PATCH] fs: record task name which froze superblock

Hi,

On 18/02/15 09:13, Jan Kara wrote:
> On Wed 18-02-15 10:34:55, Alexey Dobriyan wrote:
>> On Mon, Feb 16, 2015 at 10:38:52AM +0100, Jan Kara wrote:
>>> On Sat 14-02-15 21:55:24, Alexey Dobriyan wrote:
>>>> Freezing and thawing are separate system calls, task which is supposed
>>>> to thaw filesystem/superblock can disappear due to crash or not thaw
>>>> due to a bug. Record at least task name (we can't take task_struct
>>>> reference) to make support engineer's life easier.
>>>>
>>>> Hopefully 16 bytes per superblock isn't much.
>>>>
>>>> P.S.: Cc'ing GFS2 people just in case they want to correct
>>>> my understanding of GFS2 having async freeze code.
>>>>
>>>> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
>>>    Hum, and when do you show the task name? Or do you expect that customer
>>> takes a crashdump and support just finds it in memory?
>> Yeah, having at least something in crashdump is fine.
>    OK, then comment about this at freeze_comm[] definition so that it's
> clear it isn't just set-but-never-read field.
>   
>>>> --- a/fs/ioctl.c
>>>> +++ b/fs/ioctl.c
>>>> @@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
>>>>   static int ioctl_fsfreeze(struct file *filp)
>>>>   {
>>>>   	struct super_block *sb = file_inode(filp)->i_sb;
>>>> +	int rv;
>>>>   
>>>>   	if (!capable(CAP_SYS_ADMIN))
>>>>   		return -EPERM;
>>>> @@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
>>>>   		return -EOPNOTSUPP;
>>>>   
>>>>   	/* Freeze */
>>>> -	if (sb->s_op->freeze_super)
>>>> -		return sb->s_op->freeze_super(sb);
>>>> -	return freeze_super(sb);
>>>> +	if (sb->s_op->freeze_super) {
>>>> +		rv = sb->s_op->freeze_super(sb);
>>>> +		if (rv == 0)
>>>> +			get_task_comm(sb->s_writers.freeze_comm, current);
>>>> +	} else
>>>> +		rv = freeze_super(sb);
>>>> +	return rv;
>>>    Why don't you just set the name in ioctl_fsfreeze() in both cases?
>> There are users of freeze_super() in GFS2 unless I'm misreading code.
>    Yes, there are. The call in fs/gfs2/glops.c is in a call path from
> ->freeze_super() handler for GFS2 so that one is handled in
> ioctl_fsfreeze() anyway. The call in fs/gfs2/sys.c is a way to freeze
> filesystem via sysfs (dunno why GFS2 has to invent its own thing and ioctl
> isn't enough). Steven? So having the logic in ioctl_fsfreeze(),
> freeze_bdev() and freeze_store() in gfs2 seems to be enough.
>
The sysfs freeze thing is historical and strongly deprecated - I hope 
that we may be able to remove it one day,

Steve.

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