Re: [PATCH] hibernate: unlock swap bdev for writing when uswsusp is active

[Domenico Andreoli <domenico.andreoli@linux.com>]

On Sat, Feb 29, 2020 at 09:08:25AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.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.  The
> uswsusp ioctls allow userspace to lease parts of swap devices, so turn
> S_SWAPFILE off when invoking suspend.
> 
> Fixes: 1638045c3677 ("mm: set S_SWAPFILE on blockdev swap devices")
> Reported-by: Domenico Andreoli <domenico.andreoli@linux.com>
> Reported-by: Marian Klein <mkleinsoft@gmail.com>

I also tested it yesterday but was not satisfied, unfortunately I did
not come with my comment in time.

Yes, I confirm that the uswsusp works again but also checked that
swap_relockall() is not triggered at all and therefore after the first
hibernation cycle the S_SWAPFILE bit remains cleared and the whole
swap_relockall() is useless.

I'm not sure this patch should be merged in the current form.

Regards,
Domenico

> Tested-by: Marian Klein <mkleinsoft@gmail.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  include/linux/swap.h |    1 +
>  kernel/power/user.c  |   11 ++++++++++-
>  mm/swapfile.c        |   26 ++++++++++++++++++++++++++
>  3 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 1e99f7ac1d7e..add93e205850 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -458,6 +458,7 @@ extern void swap_free(swp_entry_t);
>  extern void swapcache_free_entries(swp_entry_t *entries, int n);
>  extern int free_swap_and_cache(swp_entry_t);
>  extern int swap_type_of(dev_t, sector_t, struct block_device **);
> +extern void swap_relockall(void);
>  extern unsigned int count_swap_pages(int, int);
>  extern sector_t map_swap_page(struct page *, struct block_device **);
>  extern sector_t swapdev_block(int, pgoff_t);
> diff --git a/kernel/power/user.c b/kernel/power/user.c
> index 77438954cc2b..b11f7037ce5e 100644
> --- a/kernel/power/user.c
> +++ b/kernel/power/user.c
> @@ -271,6 +271,8 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
>  			break;
>  		}
>  		error = hibernation_restore(data->platform_support);
> +		if (!error)
> +			swap_relockall();
>  		break;
>  
>  	case SNAPSHOT_FREE:
> @@ -372,10 +374,17 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
>  			 */
>  			swdev = new_decode_dev(swap_area.dev);
>  			if (swdev) {
> +				struct block_device *bd;
> +
>  				offset = swap_area.offset;
> -				data->swap = swap_type_of(swdev, offset, NULL);
> +				data->swap = swap_type_of(swdev, offset, &bd);
>  				if (data->swap < 0)
>  					error = -ENODEV;
> +
> +				inode_lock(bd->bd_inode);
> +				bd->bd_inode->i_flags &= ~S_SWAPFILE;
> +				inode_unlock(bd->bd_inode);
> +				bdput(bd);
>  			} else {
>  				data->swap = -1;
>  				error = -EINVAL;
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index b2a2e45c9a36..439bfb7263d3 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1799,6 +1799,32 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
>  	return -ENODEV;
>  }
>  
> +/* Re-lock swap devices after resuming from userspace suspend. */
> +void swap_relockall(void)
> +{
> +	int type;
> +
> +	spin_lock(&swap_lock);
> +	for (type = 0; type < nr_swapfiles; type++) {
> +		struct swap_info_struct *sis = swap_info[type];
> +		struct block_device *bdev = bdgrab(sis->bdev);
> +
> +		/*
> +		 * uswsusp only knows how to suspend to block devices, so we
> +		 * can skip swap files.
> +		 */
> +		if (!(sis->flags & SWP_WRITEOK) ||
> +		    !(sis->flags & SWP_BLKDEV))
> +			continue;
> +
> +		inode_lock(bdev->bd_inode);
> +		bdev->bd_inode->i_flags |= S_SWAPFILE;
> +		inode_unlock(bdev->bd_inode);
> +		bdput(bdev);
> +	}
> +	spin_unlock(&swap_lock);
> +}
> +
>  /*
>   * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
>   * corresponding to given index in swap_info (swap type).

-- 
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