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

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Date:   Sat, 1 Apr 2023 16:03:35 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>
CC:     Ye Bin <yebin10@...wei.com>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Yifan Li <yifan2.li@...el.com>
Subject: Re: [PATCH] PM: hibernate: Do not get block device exclusively in
 test_resume mode

On 2023-04-01 at 23:48:32 +0800, Chen Yu wrote:
> The system refused to do a test_resume because it found that the
> swap device has already been taken by someone else. Specificly,
> 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
> 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>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
>
Please ignore this patch, will send a refined version later. Sorry for the noise.

thanks,
Chenyu