On Wed, Mar 4, 2020 at 4:45 PM Darrick J. Wong <darrick.wong@oracle.com>
wrote:

> On Wed, Mar 04, 2020 at 09:23:27AM +0100, Domenico Andreoli wrote:
> > From: Domenico Andreoli <domenico.andreoli@linux.com>
> >
> > It turns out that there is one use case for programs being able to
> > write to swap devices, and that is the userspace hibernation code.
>
> You might want to start a separate thread for this... :)
>

Right

> Quick fix: disable the S_SWAPFILE check if hibernation is configured.
> >
> > Fixes: 1638045c3677 ("mm: set S_SWAPFILE on blockdev swap devices")
>
> Also, this should be
>
> Fixes: dc617f29dbe5 ("vfs: don't allow writes to swap files")
>

Of course

since we still want to set S_SWAPFILE on active swap devices.
>
> > Reported-by: Domenico Andreoli <domenico.andreoli@linux.com>
> > Reported-by: Marian Klein <mkleinsoft@gmail.com>
> > Signed-off-by: Domenico Andreoli <domenico.andreoli@linux.com>
> >
> > ---
> >  fs/block_dev.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > Index: b/fs/block_dev.c
> > ===================================================================
> > --- a/fs/block_dev.c
> > +++ b/fs/block_dev.c
> > @@ -2001,7 +2001,8 @@ ssize_t blkdev_write_iter(struct kiocb *
> >       if (bdev_read_only(I_BDEV(bd_inode)))
> >               return -EPERM;
> >
> > -     if (IS_SWAPFILE(bd_inode))
> > +     /* uswsusp needs to write to the swap */
> > +     if (IS_SWAPFILE(bd_inode) && !IS_ENABLED(CONFIG_HIBERNATION))
>
> ...&& hibernation_available() ?  That way we can configure this
> dynamically.
>

Then it would just be "if (IS_SWAPFILE(bd_inode) &&
!hibernation_available())", right?

Thanks for taking this on, I'll go self-NAK the revert patch I sent
> yesterday.
>

Thanks,
Dom