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

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Date:	Wed, 18 Feb 2015 10:34:55 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	swhiteho@...hat.com, cluster-devel@...hat.com
Subject: Re: [PATCH] fs: record task name which froze superblock

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.

> > --- 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.

> Also you seem to be missing freezing / thawing in freeze/thaw_bdev()
> functions.

You are correct. Resending patch (blockdev freezing tested with XFS).

> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1221,6 +1221,8 @@ struct sb_writers {
> >  	int			frozen;		/* Is sb frozen? */
> >  	wait_queue_head_t	wait_unfrozen;	/* queue for waiting for
> >  						   sb to be thawed */
> > +	/* who froze superblock */
> > +	char			freeze_comm[16];
>   Here should be TASK_COMM_LEN, shouldn't it?

It will pull sched.h, dunno if we care about headers anymore.

	Alexey
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