linux-kernel - Re: [PATCH] mm/sparsemem: fix race in accessing memory

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Date:   Thu, 26 Oct 2023 09:00:55 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Charan Teja Kalla <quic_charante@...cinc.com>
Cc:     Pavan Kondeti <quic_pkondeti@...cinc.com>, osalvador@...e.de,
        dan.j.williams@...el.com, vbabka@...e.cz,
        mgorman@...hsingularity.net, aneesh.kumar@...ux.ibm.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/sparsemem: fix race in accessing memory_section->usage

On 25.10.23 23:35, Andrew Morton wrote:
> On Tue, 17 Oct 2023 19:40:15 +0530 Charan Teja Kalla <quic_charante@...cinc.com> wrote:
> 
>>>>   		 * was allocated during boot.
>>>>   		 */
>>>>   		if (!PageReserved(virt_to_page(ms->usage))) {
>>>> +			synchronize_rcu();
>>>>   			kfree(ms->usage);
>>>>   			ms->usage = NULL;
>>>>   		}
>>> If we add NULL checks around ms->usage, this becomes
>>>
>>> tmp = rcu_replace_pointer(ms->usage, NULL, hotplug_locked());
>>> syncrhonize_rcu();
>>> kfree(tmp);
>> Per David input, I am working on using kfree_rcu().
> 
> How's it coming along?
> 
> Given that we're at 6.6-rc7 and given that this issue is causing
> daily crashes in your device farm, I'm thinking that we use the current
> version of your patch for 6.6 and for -stable.  We can look at the
> kfree_rcu() optimization for later kernel releases?

Any particular reason we have to rush this in? It's been seen by one 
company in a testing farm; there were no other reports, especially not 
from production systems. ... and the issue seems to be quite old.

-- 
Cheers,

David / dhildenb