Message-ID: <CALTww29QO5kzmN6Vd+jT=-8W5F52tJjHKSgrfUc1Z1ZAeRKHHA@mail.gmail.com>
Date: Wed, 31 Jan 2024 08:29:51 +0800
From: Xiao Ni <xni@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: mpatocka@...hat.com, heinzm@...hat.com, agk@...hat.com, snitzer@...nel.org, 
	dm-devel@...ts.linux.dev, song@...nel.org, yukuai3@...wei.com, 
	jbrassow@....redhat.com, neilb@...e.de, shli@...com, akpm@...l.org, 
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org, yi.zhang@...wei.com, 
	yangerkun@...wei.com
Subject: Re: [PATCH v4 00/14] dm-raid: fix v6.7 regressions

On Tue, Jan 30, 2024 at 10:23 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@...wei.com>
>
> Changes in v4:
>  - add patch 10 to fix a raid456 deadlock(for both md/raid and dm-raid);
>  - add patch 13 to wait for inflight IO completion while removing dm
>  device;
>
> Changes in v3:
>  - fix a problem in patch 5;
>  - add patch 12;
>
> Changes in v2:
>  - replace revert changes for dm-raid with real fixes;
>  - fix dm-raid5 deadlock that exist for a long time, this deadlock is
>  triggered because another problem is fixed in raid5, and instead of
>  deadlock, user will read wrong data before v6.7, patch 9-11;
>
> 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, md/raid behaviour, not related to
>  dm-raid;
>
> 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. And 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.
>
> There are also some other minor changes: patch 8 and patch 12;
>
> Test result:
>
> I apply this patchset on top of v6.8-rc1, and run lvm2 tests suite with
> folling cmd for 24 round(for about 2 days):
>
> for t in `ls test/shell`; do
>         if cat test/shell/$t | grep raid &> /dev/null; then
>                 make check T=shell/$t
>         fi
> done
>
> failed count                             failed test
>       1 ###       failed: [ndev-vanilla] shell/dmsecuretest.sh
>       1 ###       failed: [ndev-vanilla] shell/dmsetup-integrity-keys.sh
>       1 ###       failed: [ndev-vanilla] shell/dmsetup-keyring.sh
>       5 ###       failed: [ndev-vanilla] shell/duplicate-pvs-md0.sh
>       1 ###       failed: [ndev-vanilla] shell/duplicate-vgid.sh
>       2 ###       failed: [ndev-vanilla] shell/duplicate-vgnames.sh
>       1 ###       failed: [ndev-vanilla] shell/fsadm-crypt.sh
>       1 ###       failed: [ndev-vanilla] shell/integrity.sh
>       6 ###       failed: [ndev-vanilla] shell/lvchange-raid1-writemostlysh
>       2 ###       failed: [ndev-vanilla] shell/lvchange-rebuild-raid.sh
>       5 ###       failed: [ndev-vanilla] shell/lvconvert-raid-reshape-stripes-load-reload.sh
>       4 ###       failed: [ndev-vanilla] shell/lvconvert-raid-restripe-linear.sh
>       1 ###       failed: [ndev-vanilla] shell/lvconvert-raid1-split-trackchanges.sh
>      20 ###       failed: [ndev-vanilla] shell/lvconvert-repair-raid.sh
>      20 ###       failed: [ndev-vanilla] shell/lvcreate-large-raid.sh
>      24 ###       failed: [ndev-vanilla] shell/lvextend-raid.sh
>
> And I ramdomly pick some tests verified by hand that these test will
> fail in v6.6 as well(not all tests, I don't have the time do do this yet):
>
> shell/lvextend-raid.sh
> shell/lvcreate-large-raid.sh
> shell/lvconvert-repair-raid.sh
> shell/lvchange-rebuild-raid.sh
> shell/lvchange-raid1-writemostly.sh
>
> Yu Kuai (14):
>   md: don't ignore suspended array in md_check_recovery()
>   md: don't ignore read-only array in md_check_recovery()
>   md: make sure md_do_sync() will set MD_RECOVERY_DONE
>   md: don't register sync_thread for reshape directly
>   md: export helpers to stop sync_thread
>   dm-raid: really frozen sync_thread during suspend
>   md/dm-raid: don't call md_reap_sync_thread() directly
>   dm-raid: add a new helper prepare_suspend() in md_personality
>   md: export helper md_is_rdwr()
>   md: don't suspend the array for interrupted reshape
>   md/raid456: fix a deadlock for dm-raid456 while io concurrent with
>     reshape
>   dm-raid: fix lockdep waring in "pers->hot_add_disk"
>   dm: wait for IO completion before removing dm device
>   dm-raid: remove mddev_suspend/resume()
>
>  drivers/md/dm-raid.c |  78 +++++++++++++++++++---------
>  drivers/md/dm.c      |   3 ++
>  drivers/md/md.c      | 120 +++++++++++++++++++++++++++++--------------
>  drivers/md/md.h      |  16 ++++++
>  drivers/md/raid10.c  |  16 +-----
>  drivers/md/raid5.c   |  61 ++++++++++++----------
>  6 files changed, 190 insertions(+), 104 deletions(-)
>
> --
> 2.39.2
>

Hi all

In my environment, the lvm2 regression test has passed. There are only
three failed cases which also fail in kernel 6.6.

###       failed: [ndev-vanilla] shell/lvresize-fs-crypt.sh
###       failed: [ndev-vanilla] shell/pvck-dump.sh
###       failed: [ndev-vanilla] shell/select-report.sh
### 426 tests: 346 passed, 70 skipped, 0 timed out, 7 warned, 3 failed
  in 89:26.073

Best Regards
Xiao

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