Re: [systemd-devel] systemd-213: regression with zram

[Minchan Kim <minchan@kernel.org>]

On Tue, Jun 24, 2014 at 07:21:12AM +0000, Minchan Kim wrote:
> On Tue, Jun 24, 2014 at 12:34:50PM +0600, Alexander E. Patrakov wrote:
> > 24.06.2014 12:22, Minchan Kim wrote:
> > >
> > >Hello,
> > >
> > >Sorry for the late response.
> > 
> > Better late than never.
> > 
> > >If I parse your problem correctly, you meant that changing disksize is
> > >failed while someone opens /dev/zram0?
> > >
> > >I tried test which opens "/dev/zram0" with O_RDWR and sleep forever
> > >and then echo $((512<<20)) > /sys/block/zram0/disksize is successful.
> > >IOW, it's okay with me.
> > 
> > No, this is only a part of the problem. A valid test would be:
> > 
> > 0. Reset the unused zram device.
> > 1. Use a program that opens /dev/zram0 with O_RDWR and sleeps until killed.
> > 2. While that program sleeps, echo the correct value to
> > /sys/block/zram0/disksize.
> > 3. Verify (e.g. in /proc/partitions) that the disk size is applied
> > correctly. It is.
> > 4. While that program still sleeps, attempt to mkswap /dev/zram0.
> > This fails:
> > 
> > mkswap: error: swap area needs to be at least 40 KiB
> > 
> > There is nothing in dmesg.
> 
> Thanks. I could reproduce.
> When I read strace result, fstat access closed fd which seem to be
> a culprit.
> 
> Cced util-linux.

When I read disk-utils/mkswap.c, it's not a problem of mkswap.
The problem is ioctl(fd, BLKGETSIZE64, bytes) is not work in
your scenario. IOW, kernel fault.
Hmm,, will investgate it.

Thanks for the report!
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