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

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Date:   Wed, 12 Apr 2023 09:17:24 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     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 2023-04-11 at 18:21:36 +0200, Rafael J. Wysocki wrote:
> 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.
>
Yes, will fix it. 
> > 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"
> 
OK, will fix it. 
> > 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.
>
OK, will fix it in next version.

thanks,
Chenyu