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SubjectRe: [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@gmail.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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