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From:   "Wang, Wendy" <wendy.wang@intel.com>
To:     "Chen, Yu C" <yu.c.chen@intel.com>
CC:     "Brown, Len" <len.brown@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "yebin10@huawei.com" <yebin10@huawei.com>,
        "Li, Yifan2" <yifan2.li@intel.com>
Subject: Re: [PATCH] PM: hibernate: Do not get block device exclusively in
 test_resume mode
Thread-Topic: Re: [PATCH] PM: hibernate: Do not get block device exclusively
 in test_resume mode
Thread-Index: AdlmAUM01YqZY1GMS/O4hzI83IeadQ==
Date:   Mon, 3 Apr 2023 08:05:52 +0000
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On 2023-04-02 at 00:55:40 +0800, Chen Yu wrote:=20
> 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.
>=20
> Steps to reproduce:
>  dd if=3D/dev/zero of=3D/swapfile bs=3D$(cat /proc/meminfo |=20
>        awk '/MemTotal/ {print $2}') count=3D1024 conv=3Dnotrunc
>  mkswap /swapfile
>  swapon /swapfile
>  swap-offset /swapfile
>  echo 34816 > /sys/power/resume_offset
>  echo test_resume > /sys/power/disk
>  echo disk > /sys/power/state
>=20
>  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)
>=20
> 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 th=
e
> test_resume mode. Because when test_resume happens, the block device has
> been mounted already.
>=20
> 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 swsu=
sp_check()")
> is unlikely to happen.
>=20
> Fixes: 39fbef4b0f77 ("PM: hibernate: Get block device exclusively in swsu=
sp_check()")
> Reported-by: Yifan Li <yifan2.li@intel.com>
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>
>
Tested on Intel EMR, PASS.=20
Tested-by: Wendy Wang <wendy.wang@intel.com>