FAILED: patch "[PATCH] mm: hugetlb: return -ENOSPC on memcg charge failure" failed to apply to 6.18-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 956aeff185e7e16b989202bde0bb29859adba99d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107050856-failed-6.18-956aeff185e7@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 956aeff185e7e16b989202bde0bb29859adba99d Mon Sep 17 00:00:00 2001
From: Ackerley Tng <ackerleytng@google.com>
Date: Wed, 9 Sep 2026 10:11:00 -0700
Subject: [PATCH] mm: hugetlb: return -ENOSPC on memcg charge failure

Patch series "Fix bugs in HugeTLB allocation when
mem_cgroup_charge_hugetlb() fails", v2.

In hugetlb_alloc_folio(), when mem_cgroup_charge_hugetlb() fails, there
are 2 issues:

1. free_huge_folio() expects a non-refcounted folio and will
   VM_BUG_ON_FOLIO().

2. -ENOMEM is returned, causing an infinite loop retrying the fault.


This patch (of 2):

When mem_cgroup_charge_hugetlb() fails with -ENOMEM, alloc_hugetlb_folio()
currently propagates this error.  This results in the page fault handler
returning VM_FAULT_OOM.

Because HugeTLB allocations are high-order and use __GFP_RETRY_MAYFAIL,
they bypass the OOM killer.  Returning VM_FAULT_OOM to the #PF handler
without triggering the OOM killer (or having it make progress) leads to an
infinite loop of retrying the fault.

Avoid this loop by returning -ENOSPC when charging fails, which maps to
VM_FAULT_SIGBUS, terminating the process cleanly.

Make mem_cgroup_charge_hugetlb() fault handling use a common error
handling path, the same handling used for
hugetlb_cgroup_uncharge_cgroup{,_rsvd}(), which also don't trigger the OOM
killer and hence opt to terminate the process with a SIGBUS.

Link: https://lore.kernel.org/20260909-hugetlb-alloc-folio-memcg-charge-error-handling-v2-1-4b4a8a19a7f7@google.com
Fixes: 991135774c0e ("memcg/hugetlb: introduce mem_cgroup_charge_hugetlb")
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Dongliang Mu <dzm91@hust.edu.cn>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Hongxiang Lou <louhongxiang@huawei.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Ma Wupeng <mawupeng1@huawei.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vishal Annapurve <vannapurve@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Yanteng Si <si.yanteng@linux.dev>
Cc: <stable@vger.kernel.org>
---
 mm/hugetlb.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 84552c993cbbb..a16d04aae6196 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2851,7 +2851,6 @@ void wait_for_freed_hugetlb_folios(void)
  *
  * Return: A pointer to the allocated folio, or an ERR_PTR on failure.
  *         -ENOSPC if cgroup charging fails or no folio is available.
- *         -ENOMEM if mem cgroup charging fails.
  */
 struct folio *hugetlb_alloc_folio(struct hstate *h,
 		struct mempolicy_interpreted *mpoli, u8 alloc_flags)
@@ -2924,7 +2923,11 @@ struct folio *hugetlb_alloc_folio(struct hstate *h,
 		 * were committed to the folio and freeing the folio
 		 * would have cleared those up.
 		 */
-		return ERR_PTR(ret);
+		/*
+		 * Return -ENOSPC, since retrying the fault is futile:
+		 * the OOM killer is not triggered for HugeTLB.
+		 */
+		return ERR_PTR(-ENOSPC);
 	}
 
 	return folio;
-- 
2.53.0