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

[Steven Whitehouse]

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@xxxxxxxxx>
> > >    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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