linux-kernel - Re: [PATCH v2 2/2] PM: hibernate: Do not get block device exclusively in test

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Date:   Tue, 11 Apr 2023 18:21:36 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Ye Bin <yebin10@...wei.com>,
        Pavankumar Kondeti <quic_pkondeti@...cinc.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yifan Li <yifan2.li@...el.com>
Subject: Re: [PATCH v2 2/2] PM: hibernate: Do not get block device exclusively
 in test_resume mode

On Tue, Apr 11, 2023 at 6:23 AM Chen Yu <yu.c.chen@...el.com> wrote:
>
> The system refused to do a test_resume because it found that the
> swap device has already been taken by someone else. Specificly,

"Specifically" I suppose.

> the swsusp_check()->blkdev_get_by_dev(FMODE_EXCL) is supposed to
> do this check.
>
> Steps to reproduce:
>  dd if=/dev/zero of=/swapfile bs=$(cat /proc/meminfo |
>        awk '/MemTotal/ {print $2}') count=1024 conv=notrunc
>  mkswap /swapfile
>  swapon /swapfile
>  swap-offset /swapfile
>  echo 34816 > /sys/power/resume_offset
>  echo test_resume > /sys/power/disk
>  echo disk > /sys/power/state
>
>  PM: Using 3 thread(s) for compression
>  PM: Compressing and saving image data (293150 pages)...
>  PM: Image saving progress:   0%
>  PM: Image saving progress:  10%
>  ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
>  ata1.00: configured for UDMA/100
>  ata2: SATA link down (SStatus 0 SControl 300)
>  ata5: SATA link down (SStatus 0 SControl 300)
>  ata6: SATA link down (SStatus 0 SControl 300)
>  ata3: SATA link down (SStatus 0 SControl 300)
>  ata4: SATA link down (SStatus 0 SControl 300)
>  PM: Image saving progress:  20%
>  PM: Image saving progress:  30%
>  PM: Image saving progress:  40%
>  PM: Image saving progress:  50%
>  pcieport 0000:00:02.5: pciehp: Slot(0-5): No device found
>  PM: Image saving progress:  60%
>  PM: Image saving progress:  70%
>  PM: Image saving progress:  80%
>  PM: Image saving progress:  90%
>  PM: Image saving done
>  PM: hibernation: Wrote 1172600 kbytes in 2.70 seconds (434.29 MB/s)
>  PM: S|
>  PM: hibernation: Basic memory bitmaps freed
>  PM: Image not found (code -16)
>
> This is because when using the swapfile as the hibernation storage,
> the block device where the swapfile is located has already been mounted
> by the OS distribution(usually been mounted as the rootfs). This is not

"usually mounted"

> an issue for normal hibernation, because software_resume()->swsusp_check()
> happens before the block device(rootfs) mount. But it is a problem for the
> test_resume mode. Because when test_resume happens, the block device has
> been mounted already.
>
> Thus remove the FMODE_EXCL for test_resume mode. This would not be a
> problem because in test_resume stage, the processes have already been
> frozen, and the race condition described in
> Commit 39fbef4b0f77 ("PM: hibernate: Get block device exclusively in swsusp_check()")
> is unlikely to happen.
>
> Fixes: 39fbef4b0f77 ("PM: hibernate: Get block device exclusively in swsusp_check()")
> Reported-by: Yifan Li <yifan2.li@...el.com>
> Suggested-by: Pavankumar Kondeti <quic_pkondeti@...cinc.com>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
>  kernel/power/hibernate.c | 5 +++--
>  kernel/power/swap.c      | 5 +++--
>  2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index aa551b093c3f..defc2257b052 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -688,18 +688,19 @@ static int load_image_and_restore(void)
>  {
>         int error;
>         unsigned int flags;
> +       fmode_t mode = snapshot_test ? FMODE_READ : (FMODE_READ | FMODE_EXCL);

fmode_t mode = FMODE_READ;

if (snapshot_test)
        mode |= FMODE_EXCL;

pretty please, and analogously below.

>
>         pm_pr_dbg("Loading hibernation image.\n");
>
>         lock_device_hotplug();
>         error = create_basic_memory_bitmaps();
>         if (error) {
> -               swsusp_close(FMODE_READ | FMODE_EXCL);
> +               swsusp_close(mode);
>                 goto Unlock;
>         }
>
>         error = swsusp_read(&flags);
> -       swsusp_close(FMODE_READ | FMODE_EXCL);
> +       swsusp_close(mode);
>         if (!error)
>                 error = hibernation_restore(flags & SF_PLATFORM_MODE);
>
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 36a1df48280c..0f699cd96a89 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -1518,9 +1518,10 @@ int swsusp_check(void)
>  {
>         int error;
>         void *holder;
> +       fmode_t mode = snapshot_test ? FMODE_READ : (FMODE_READ | FMODE_EXCL);
>
>         hib_resume_bdev = blkdev_get_by_dev(swsusp_resume_device,
> -                                           FMODE_READ | FMODE_EXCL, &holder);
> +                                           mode, &holder);
>         if (!IS_ERR(hib_resume_bdev)) {
>                 set_blocksize(hib_resume_bdev, PAGE_SIZE);
>                 clear_page(swsusp_header);
> @@ -1547,7 +1548,7 @@ int swsusp_check(void)
>
>  put:
>                 if (error)
> -                       blkdev_put(hib_resume_bdev, FMODE_READ | FMODE_EXCL);
> +                       blkdev_put(hib_resume_bdev, mode);
>                 else
>                         pr_debug("Image signature found, resuming\n");
>         } else {
> --