linux-kernel - RE: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

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Date:   Fri, 5 Mar 2021 15:55:25 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Aili Yao <yaoaili@...gsoft.com>
CC:     HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>, Oscar Salvador <osalvador@...e.de>,
        "david@...hat.com" <david@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "yangfeng1@...gsoft.com" <yangfeng1@...gsoft.com>
Subject: RE: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

> From the walk, it seems we have got the virtual address, can we just send a SIGBUS with it?

If the walk wins the race and the pte for the poisoned page is still valid, then yes.

But we could have:

CPU1                            CPU2
memory_failure sets poison
bit for struct page


rmap finds page in task
on CPU2 and sets PTE
to not-valid-poison

                                memory_failure returns
                                early because struct page
                                already marked as poison

                                walk page tables looking
                                for mapping - don't find it

-Tony