From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C74883BA222; Tue, 9 Jun 2026 16:16:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=82.195.75.108 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781021796; cv=none; b=aLTTPCbaS7tx8ggLkqvSpH1/tCeAj96cfXSO0kLVVzsRinOe9ielE7a1TDG9TegQEc2xU4O0ybSLNvZ1Cck2vlTQsYOErk8ZmQ+RNN0yHwHg4AMeQ0sXEhf/OCIQ7iFrJWOaaPAJLMGTO1B7hIl/wE1O6sHIYoiyXtWPDxAHlts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781021796; c=relaxed/simple; bh=558L1ra+dBxaD/r4YWvIOQvdm4T/8f3GLfBJYj9OeXo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SYxlkQ3+vy3YXPFoFf7xt9Vr6WDiH6OS3YpnsKQ+YC/Z5phweCWjAEk6pesRwJX7uTBYcDWqaK31cnXxeZ/41YOIh/lGUAZL/SqHpPgSDbAZ0TpirBjF9y6emyF4RuzWL84BK+BEv0gRYZVEKZ/JwtkGA2tb5UzvKCZqV0BGAOE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org; spf=pass smtp.mailfrom=debian.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b=KCMiFdDQ; arc=none smtp.client-ip=82.195.75.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=debian.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b="KCMiFdDQ" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=99lfJJqgGV+EWW3BmhkNn6qfLnQ2f2pBi7n0sNfkhRc=; b=KCMiFdDQRjj3L4VP/YosTAJIHo A1HbCUZVuYN7QbDdovs+Eez4e7YWDN+MESTqcmSKS0X6xUE+/AB4Y5lJHiz4InUoPPj+XMC/hNkIt SioyR/IQr8KNLhMSRH3hkQYgLUjy0MRbm2DjaC0AvRXaMOmnFidXdYk7mFLsSOrzNMMOmQ/LJpl8i nuiqHmuYaSIWoHJjOT8sCdtQYwbS7cZgmqX5m7G9eEmq9xw7YOJ6gbnSImVGYELlJCN5W7MqHe6y8 x+dP6G3HTloYyhhFNFNGEJlk+s/4eVl+CagKaZMtwcfdmNv+j22FgaAjBLqep+zJea+ZaVcfsyC2W 5NT40grw==; Received: from authenticated-user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1wWz75-008WX7-3A; Tue, 09 Jun 2026 16:15:40 +0000 Date: Tue, 9 Jun 2026 09:15:33 -0700 From: Breno Leitao To: "David Hildenbrand (Arm)" Cc: Miaohe Lin , Andrew Morton , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Naoya Horiguchi , Jonathan Corbet , Shuah Khan , "Liam R. Howlett" , lance.yang@linux.dev, Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-trace-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v9 2/6] mm/memory-failure: surface unhandlable kernel pages as -ENOTRECOVERABLE Message-ID: References: <20260609-ecc_panic-v9-0-432a74002e74@debian.org> <20260609-ecc_panic-v9-2-432a74002e74@debian.org> <174b8d76-5514-4942-af5d-c975ff95ee03@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <174b8d76-5514-4942-af5d-c975ff95ee03@kernel.org> X-Debian-User: leitao On Tue, Jun 09, 2026 at 04:41:01PM +0200, David Hildenbrand (Arm) wrote: > On 6/9/26 12:56, Breno Leitao wrote: > > get_any_page() collapses every HWPoisonHandlable() rejection into a > > single -EIO via the __get_hwpoison_page() -> -EBUSY -> shake_page() > > -> retry path. That is correct for the transient case (a userspace > > folio briefly off LRU during migration or compaction, which a later > > shake can drag back), but wrong for stable kernel-owned pages: slab, > > page-table, large-kmalloc and PG_reserved pages will never become > > HWPoisonHandlable(), so the retry loop is wasted work and the final > > -EIO loses the "this is structurally unrecoverable" information. > > memory_failure() then maps -EIO into MF_MSG_GET_HWPOISON, which the > > panic-on-unrecoverable sysctl deliberately does not act on. > > > > Introduce HWPoisonKernelOwned(), a small predicate that positively > > identifies pages the hwpoison handler cannot recover from: > > > > HWPoisonKernelOwned(p, flags) := > > !(MF_SOFT_OFFLINE && page_has_movable_ops(p)) && > > (PageReserved(p) || > > PageSlab(head) || PageTable(head) || PageLargeKmalloc(head)) > > > > where head = compound_head(p). > > > > PG_reserved is a per-page flag (PF_NO_COMPOUND) and is tested on the > > page directly. The slab, page-table and large-kmalloc page-type bits > > are only stored on the head page, so those tests resolve the compound > > head first, then re-read compound_head(page) afterwards: a concurrent > > split or compound free that moves head invalidates the just-read flags > > and the loop retries. The lookup still takes no refcount, mirroring > > the rest of get_any_page(); the recheck closes the common split race, > > and a residual free->alloc->free in the same window can only mis-tag > > a genuinely poisoned page, never reclassify a handlable one. > > > > The MF_SOFT_OFFLINE / page_has_movable_ops() opt-out mirrors the > > same exception in HWPoisonHandlable(): soft-offline is allowed to > > migrate movable_ops pages even though they are not on the LRU, and > > we must not pre-empt that with an unrecoverable verdict. > > > > The list is intentionally not exhaustive. vmalloc and kernel-stack > > pages, for example, do not carry a page_type bit and would need a > > different oracle; they keep going through the existing retry path > > unchanged. This is the smallest set we can identify with certainty > > by page type. > > > > Wire the helper into the top of get_any_page() to short-circuit > > those pages before the retry loop runs. On a hit, drop the caller's > > MF_COUNT_INCREASED reference (if any) and return -ENOTRECOVERABLE > > straight away. Pages outside the helper's positive list still take > > the existing retry path and return -EIO, leaving operator-visible > > behaviour for those cases unchanged. > > > > Extend the unhandlable-page pr_err() to fire for either errno and > > update the get_hwpoison_page() kerneldoc to document the new return. > > > > memory_failure() still folds every negative return into > > MF_MSG_GET_HWPOISON via its existing "else if (res < 0)" branch, so > > this patch on its own only changes the errno that soft_offline_page() > > can propagate to its callers. A follow-up wires -ENOTRECOVERABLE > > through memory_failure() and reports MF_MSG_KERNEL for the > > unrecoverable cases, which is what the > > panic_on_unrecoverable_memory_failure sysctl observes. > > > > Suggested-by: David Hildenbrand > > Suggested-by: Lance Yang > > Signed-off-by: Breno Leitao > > --- > > mm/memory-failure.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 58 insertions(+), 2 deletions(-) > > > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > > index f4d3e6e20e13..eed9de387694 100644 > > --- a/mm/memory-failure.c > > +++ b/mm/memory-failure.c > > @@ -1325,6 +1325,46 @@ static inline bool HWPoisonHandlable(struct page *page, unsigned long flags) > > return PageLRU(page) || is_free_buddy_page(page); > > } > > > > +/* > > + * Positive identification of pages the hwpoison handler cannot recover. > > + * These page types are owned by kernel internals (no userspace mapping > > + * to unmap, no file mapping to invalidate, no migration target), so the > > + * shake_page() / retry loop in get_any_page() can never turn them into > > + * something HWPoisonHandlable() will accept. Short-circuit them to > > + * -ENOTRECOVERABLE so callers can panic on operator request instead of > > + * spinning through retries that exit as a transient-looking -EIO. > > + * > > + * The MF_SOFT_OFFLINE / page_has_movable_ops() opt-out mirrors > > + * HWPoisonHandlable(): soft-offline is allowed to migrate movable_ops > > + * pages even though they are not on the LRU. > > + */ > > +static inline bool HWPoisonKernelOwned(struct page *page, unsigned long flags) > > +{ > > + struct page *head; > > + > > + if ((flags & MF_SOFT_OFFLINE) && page_has_movable_ops(page)) > > + return false; > > + > > On a second look: Do we really need that? The page types below never support > migration. So I guess that check is not required? > > Apart from that, looks good with two comments: > > a) HWPoisonKernelOwned: this is not the common style for us to name functions. > > is_kernel_owned_page() or sth like that would do. Ack, I will rename it is_kernel_owned_page() In my defence, most of the functions similar to HWPoisonKernelOwned() has this name format, and I got this discussion earlier (with Lance? I think). Here are the similar function names in that file: * HWPoisonHandlable * PageHWPoisonTakenOff() * SetPageHWPoisonTakenOff I will update in the new version. > b) The function doc can likely be simplified a bit. No need to mention the > short-circuit stuff, for example, IMHO. Ack Thanks for the review, --breno