Re: [PATCH v2 00/11] dm-raid: fix v6.7 regressions

[Yu Kuai]

Hi,

在 2024/01/25 8:46, Song Liu 写道:
> On Wed, Jan 24, 2024 at 1:18 AM Yu Kuai <yukuai3@xxxxxxxxxx> wrote:
> > First regression related to stop sync thread:
> >
> > The lifetime of sync_thread is designed as following:
> >
> > 1) Decide want to start sync_thread, set MD_RECOVERY_NEEDED, and wake up
> > daemon thread;
> > 2) Daemon thread detect that MD_RECOVERY_NEEDED is set, then set
> > MD_RECOVERY_RUNNING and register sync_thread;
> > 3) Execute md_do_sync() for the actual work, if it's done or
> > interrupted, it will set MD_RECOVERY_DONE and wake up daemone thread;
> > 4) Daemon thread detect that MD_RECOVERY_DONE is set, then clear
> > MD_RECOVERY_RUNNING and unregister sync_thread;
> >
> > In v6.7, we fix md/raid to follow this design by commit f52f5c71f3d4
> > ("md: fix stopping sync thread"), however, dm-raid is not considered at
> > that time, and following test will hang:
> >
> > shell/integrity-caching.sh
> > shell/lvconvert-raid-reshape.sh
> >
> > This patch set fix the broken test by patch 1-4;
> >   - patch 1 fix that step 4) is broken by suspended array;
> >   - patch 2 fix that step 4) is broken by read-only array;
> >   - patch 3 fix that step 3) is broken that md_do_sync() doesn't set
> >   MD_RECOVERY_DONE; Noted that this patch will introdece new problem that
> >   data will be corrupted, which will be fixed in later patches.
> >   - patch 4 fix that setp 1) is broken that sync_thread is register and
> >   MD_RECOVERY_RUNNING is set directly;
> >
> > With patch 1-4, the above test won't hang anymore, however, the test
> > will still fail and complain that ext4 is corrupted;
> >
> > Second regression related to frozen sync thread:
> >
> > Noted that for raid456, if reshape is interrupted, then call
> > "pers->start_reshape" will corrupt data. This is because dm-raid rely on
> > md_do_sync() doesn't set MD_RECOVERY_DONE so that new sync_thread won't
> > be registered, and patch 3 just break this.
> >
> >   - Patch 5-6 fix this problem by interrupting reshape and frozen
> >   sync_thread in dm_suspend(), then unfrozen and continue reshape in
> > dm_resume(). It's verified that dm-raid tests won't complain that
> > ext4 is corrupted anymore.
> >   - Patch 7 fix the problem that raid_message() call
> >   md_reap_sync_thread() directly, without holding 'reconfig_mutex'.
> >
> > Last regression related to dm-raid456 IO concurrent with reshape:
> >
> > For raid456, if reshape is still in progress, then IO across reshape
> > position will wait for reshape to make progress. However, for dm-raid,
> > in following cases reshape will never make progress hence IO will hang:
> >
> > 1) the array is read-only;
> > 2) MD_RECOVERY_WAIT is set;
> > 3) MD_RECOVERY_FROZEN is set;
> >
> > After commit c467e97f079f ("md/raid6: use valid sector values to determine
> > if an I/O should wait on the reshape") fix the problem that IO across
> > reshape position doesn't wait for reshape, the dm-raid test
> > shell/lvconvert-raid-reshape.sh start to hang at raid5_make_request().
> >
> > For md/raid, the problem doesn't exist because:
> >
> > 1) If array is read-only, it can switch to read-write by ioctl/sysfs;
> > 2) md/raid never set MD_RECOVERY_WAIT;
> > 3) If MD_RECOVERY_FROZEN is set, mddev_suspend() doesn't hold
> >     'reconfig_mutex' anymore, it can be cleared and reshape can continue by
> >     sysfs api 'sync_action'.
> >
> > However, I'm not sure yet how to avoid the problem in dm-raid yet.
> >
> >   - patch 9-11 fix this problem by detecting the above 3 cases in
> >   dm_suspend(), and fail those IO directly.
> >
> > If user really meet the IO error, then it means they're reading the wrong
> > data before c467e97f079f. And it's safe to read/write the array after
> > reshape make progress successfully.
>
> c467e97f079f got back ported to stable kernels (6.6.13, for example). We
> will need some fixes for them (to fix shell/lvconvert-raid-reshape.sh).
>
> Mikulas and folks, please help review the analysis above and dm-raid
> changes. The failure was triggered by c467e97f079f. However, the commit
> is doing the right thing, so we really shouldn't revert it.
>
> > Tests:
> >
> > I already run the following two tests many times and verified that they
> > won't fail anymore:
> >
> > shell/integrity-caching.sh
> > shell/lvconvert-raid-reshape.sh
>
> shell/lvconvert-raid-reshape-linear_to_raid6-single-type.sh is failing
> with upstream + this set. (I need to fix some trivial compilation errors,
> which are probably last minute typos).

I'm running test for this patchset overnight in my vm, and this test has
been ran for 9 times and all passed. Looks like I can't reporduce this
in my vm.

Thanks,
Kuai

> Thanks,
> Song
>
> .