Hi,
在 2024/02/19 15:10, Xiao Ni 写道:
On Sun, Feb 18, 2024 at 4:48 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
Hi,
在 2024/02/18 16:07, Xiao Ni 写道:
On Sun, Feb 18, 2024 at 2:22 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
Hi,
在 2024/02/18 13:07, Xiao Ni 写道:
On Sun, Feb 18, 2024 at 11:24 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
Hi,
在 2024/02/18 11:15, Xiao Ni 写道:
On Sun, Feb 18, 2024 at 10:34 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
Hi,
在 2024/02/18 10:27, Xiao Ni 写道:
On Sun, Feb 18, 2024 at 9:46 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
Hi,
在 2024/02/18 9:33, Xiao Ni 写道:
The deadlock problem mentioned in this patch should not be right?
No, I think it's right. Looks like you are expecting other problems,
like mentioned in patch 6, to be fixed by this patch.
Hi Kuai
Could you explain why step1 and step2 from this comment can happen
simultaneously? From the log, the process should be
The process is :
dev_remove->dm_destroy->__dm_destroy->dm_table_postsuspend_targets(raid_postsuspend)
-> dm_table_destroy(raid_dtr).
After suspending the array, it calls raid_dtr. So these two functions
can't happen simultaneously.
You're removing the target directly, however, dm can suspend the disk
directly, you can simplily:
1) dmsetup suspend xxx
2) dmsetup remove xxx
For dm-raid, the design of suspend stops sync thread first and then it
calls mddev_suspend to suspend array. So I'm curious why the sync
thread can still exit when array is suspended. I know the reason now.
Because before f52f5c71f (md: fix stopping sync thread), the process
is raid_postsuspend->md_stop_writes->__md_stop_writes
(__md_stop_writes sets MD_RECOVERY_FROZEN). In patch f52f5c71f, it
doesn't set MD_RECOVERY_FROZEN in __md_stop_writes anymore.
The process changes to
1. raid_postsuspend->md_stop_writes->__md_stop_writes->stop_sync_thread
(wait until MD_RECOVERY_RUNNING clears)
2. md thread -> md_check_recovery -> unregister_sync_thread ->
md_reap_sync_thread (clears MD_RECOVERY_RUNNING, stop_sync_thread
returns, md_reap_sync_thread sets MD_RECOVERY_NEEDED)
3. raid_postsuspend->mddev_suspend
4. md sync thread starts again because __md_stop_writes doesn't set
MD_RECOVERY_FROZEN.
It's the reason why we can see sync thread still happens when raid is suspended.
So the patch fix this problem should:
As I said, this is really a different problem from this patch, and it is
fixed seperately by patch 9. Please take a look at that patch.
I think we're talking about the same problem. In patch07 it has a new
api md_frozen_sync_thread. It sets MD_RECOVERY_FROZEN before
stop_sync_thread. This is right. If we use this api in
raid_postsuspend, sync thread can't restart. So the deadlock can't
happen anymore?
We are not talking about the same problem at all. This patch just fix a
simple problem in md/raid(not dm-raid). And the deadlock can also be
triggered for md/raid the same.
- mddev_suspend() doesn't handle sync_thread at all;
- md_check_recovery() ignore suspended array;
Please keep in mind this patch just fix the above case. The deadlock in
dm-raid is just an example of problems caused by this. Fix the deadlock
other way doesn't mean this case is fine.
Because this patch set is used to fix dm raid deadlocks. But this
patch changes logic, it looks like more a feature - "we can start/stop
sync thread when array is suspended". Because this patch is added many
years ago and dm raid works well. If we change this, there is
possibilities to introduce new problems. Now we should try to walk
slowly.
This patch itself really is quite simple, it fixes problems for md/raid,
and can be triggered by dm-raid as well. This patch will be needed
regardless of dm-raid, and it's absolutely not a feature.
Hi Kuai
Yes, this patch is simple. But it changes the original logic. Do we
really need to do this? And as the title of the patch set, it's used
Nothing is changed, this patch itself fix a long term regression. And I
already change the title to fix dm-raid and md/raid regressions.
to fix regression problems. We need to avoid much changes, find out
the root cause and fix them. It's better to use another patch set to
do more jobs. For example, allow sync request when array is suspended
(But I don't want to do this change).
Following behaviour is not changed with this patchset:
1. dm-raid should stop and frozen sync_thread during suspend;
2. sync_thread can still runing while md/raid is suspended; And my point
is that if you want to forbit new sync_thread, use MD_REOCVERY_FROZEN
instead of suspended;
For dm-raid, there is no doubt that sync_thread should be stopped before
suspend, and keep frozen until resume, and this behaviour is not changed
Agree with this
at all and will never change. Other patches actually tries to gurantee
In fact, we only need to use one line code to do this. We don't need
so many patches. It only needs to set MD_RECOVERY_FROZEN before stop
sync thread.
set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
I agree this make sense, but as I said in the other thread, this is not
enough.
__md_stop_writes(mddev);
this. If you think this patch can introduce new problems for dm-raid,
please be more specific.
The problem in dm-raid is that it relies on __md_stop_writes() to stop
and frozen sync_thread, while it also relies that MD_RECOVERY_FROZEN is
not set, and this is abuse of MD_RECOVERY_FROZEN. And if you still think
there are problems with considering of the entire patchset, feel free to
discuss. :)
In fact, dmraid sets MD_RECOVERY_FROZEN before f52f5c71f3d4 (md: fix
stopping sync thread). It calls __md_stop_writes and this function
sets MD_RECOVERY_FROZEN. Thanks for your patience :)
I know that, and f52f5c71f3d4 really should set MD_RECOVERY_FROZEN. But
looks like you want to keep the way it used to be, and you don't want to
fix problems that exist in dm-raid for a long term.
If you send your patches before this, I'll be happy to accept them.
However, I know this patchest might be complicated, but I already did
the hard work, and I think this patchset fix the regressions in a better
way, and I'm trying to let dm-raid and md/raid to manage sync_thread the
same safer way.
So far, I think all problems that you concerned are all fixed with this
patchset, and as I said, I'll be happy to dissuss if you think there are
other problems with this patchset.
Thanks,
Kuai
Regards
Xiao
Thanks,
Kuai
.
