Re: [BUG REPORT] mm/damon: softlockup when kdamond walk page with cpu hotplug

[SeongJae Park]

On Thu, 18 Sep 2025 01:52:49 -0700 SeongJae Park <sj@xxxxxxxxxx> wrote:

> Hello,
> 
> On Thu, 18 Sep 2025 03:00:29 +0000 Xinyu Zheng <zhengxinyu6@xxxxxxxxxx> wrote:
> 
> > A softlockup issue was found with stress test:
[...]
> damon_mkold_pmd_entry() calls pte_offset_map_lock().  If the call returns an
> error, damon_mkold_pmd_entry() sets walk->action as ACTION_AGAIN, to retry.  If
> the pte_offset_map_lock() continues fails, infinite loop can happen.  I
> understand the loop you mentioned above is this case.
> 
> The error handling (retrying) was introduced by commit 7780d04046a2
> ("mm/pagewalkers: ACTION_AGAIN if pte_offset_map_lock() fails").

I added Hugh to this thread from the original mail of this reply, because he is
the author of the commit.  I should clarified this on the original mail but
forgot saying that, sorry.


Thanks,
SJ

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