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

Domenico Andreoli
2020-02-29T18:07:22Z

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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