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From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, alex.shi@linux.alibaba.com,
	cai@lca.pw, hannes@cmpxchg.org, hughd@google.com,
	linux-mm@kvack.org, mhocko@suse.com, mike.kravetz@oracle.com,
	mm-commits@vger.kernel.org, shakeelb@google.com,
	shy828301@gmail.com, stable@vger.kernel.org,
	torvalds@linux-foundation.org
Subject: [patch 04/15] shmem: shmem_writepage() split unlikely i915 THP
Date: Fri, 18 Sep 2020 21:20:09 -0700
Message-ID: <20200919042009.bomzxmrg7%akpm@linux-foundation.org> (raw)
In-Reply-To: <20200918211925.7e97f0ef63d92f5cfe5ccbc5@linux-foundation.org>

From: Hugh Dickins <hughd@google.com>
Subject: shmem: shmem_writepage() split unlikely i915 THP

drivers/gpu/drm/i915/gem/i915_gem_shmem.c contains a shmem_writeback()
which calls shmem_writepage() from a shrinker: that usually works well
enough; but if /sys/kernel/mm/transparent_hugepage/shmem_enabled has been
set to "force" (documented as "Force the huge option on for all - very
useful for testing"), shmem_writepage() is surprised to be called with a
huge page, and crashes on the VM_BUG_ON_PAGE(PageCompound) (I did not find
out where the crash happens when CONFIG_DEBUG_VM is off).

LRU page reclaim always splits the shmem huge page first: I'd prefer not
to demand that of i915, so check and split compound in shmem_writepage().

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008301401390.5954@eggly.anvils
Fixes: 2d6692e642e7 ("drm/i915: Start writeback from the shrinker")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Yang Shi <shy828301@gmail.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Qian Cai <cai@lca.pw>
Cc: <stable@vger.kernel.org>	[5.3+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/mm/shmem.c~shmem-shmem_writepage-split-unlikely-i915-thp
+++ a/mm/shmem.c
@@ -1362,7 +1362,15 @@ static int shmem_writepage(struct page *
 	swp_entry_t swap;
 	pgoff_t index;
 
-	VM_BUG_ON_PAGE(PageCompound(page), page);
+	/*
+	 * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "force",
+	 * then drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages,
+	 * and its shmem_writeback() needs them to be split when swapping.
+	 */
+	if (PageTransCompound(page))
+		if (split_huge_page(page) < 0)
+			goto redirty;
+
 	BUG_ON(!PageLocked(page));
 	mapping = page->mapping;
 	index = page->index;
_

  parent reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-19  4:19 incoming Andrew Morton
2020-09-19  4:20 ` [patch 01/15] mailmap: add older email addresses for Kees Cook Andrew Morton
2020-09-19  4:20 ` [patch 02/15] ksm: reinstate memcg charge on copied pages Andrew Morton
2020-09-19  4:20 ` [patch 03/15] mm: migration of hugetlbfs page skip memcg Andrew Morton
2020-09-19  4:20 ` Andrew Morton [this message]
2020-09-19  4:20 ` [patch 05/15] mm: fix check_move_unevictable_pages() on THP Andrew Morton
2020-09-19  4:20 ` [patch 06/15] mlock: fix unevictable_pgs event counts " Andrew Morton
2020-09-19  4:20 ` [patch 07/15] tmpfs: restore functionality of nr_inodes=0 Andrew Morton
2020-09-19  4:20 ` [patch 08/15] kprobes: fix kill kprobe which has been marked as gone Andrew Morton
2020-09-19  4:20 ` [patch 09/15] mm/thp: fix __split_huge_pmd_locked() for migration PMD Andrew Morton
2020-09-19  4:20 ` [patch 10/15] selftests/vm: fix display of page size in map_hugetlb Andrew Morton
2020-09-19  4:20 ` [patch 11/15] mm/memory_hotplug: drain per-cpu pages again during memory offline Andrew Morton
2020-09-19  4:20 ` [patch 12/15] ftrace: let ftrace_enable_sysctl take a kernel pointer buffer Andrew Morton
2020-09-19  4:20 ` [patch 13/15] stackleak: let stack_erasing_sysctl " Andrew Morton
2020-09-19  4:20 ` [patch 14/15] fs/fs-writeback.c: adjust dirtytime_interval_handler definition to match prototype Andrew Morton
2020-09-19  4:20 ` [patch 15/15] kcsan: kconfig: move to menu 'Generic Kernel Debugging Instruments' Andrew Morton

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