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From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, apopple@nvidia.com, hughd@google.com,
	jack@suse.cz, juew@google.com, kirill.shutemov@linux.intel.com,
	linmiaohe@huawei.com, linux-mm@kvack.org, minchan@kernel.org,
	mm-commits@vger.kernel.org, naoya.horiguchi@nec.com,
	osalvador@suse.de, peterx@redhat.com, rcampbell@nvidia.com,
	shakeelb@google.com, shy828301@gmail.com, stable@vger.kernel.org,
	torvalds@linux-foundation.org, wangyugui@e16-tech.com,
	willy@infradead.org, ziy@nvidia.com
Subject: [patch 17/18] mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split
Date: Tue, 15 Jun 2021 18:24:07 -0700	[thread overview]
Message-ID: <20210616012407.gaQGkGzcu%akpm@linux-foundation.org> (raw)
In-Reply-To: <20210615182248.9a0ba90e8e66b9f4a53c0d23@linux-foundation.org>

From: Yang Shi <shy828301@gmail.com>
Subject: mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split

When debugging the bug reported by Wang Yugui [1], try_to_unmap() may
fail, but the first VM_BUG_ON_PAGE() just checks page_mapcount() however
it may miss the failure when head page is unmapped but other subpage is
mapped.  Then the second DEBUG_VM BUG() that check total mapcount would
catch it.  This may incur some confusion.  And this is not a fatal issue,
so consolidate the two DEBUG_VM checks into one VM_WARN_ON_ONCE_PAGE().

[1] https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/

Link: https://lkml.kernel.org/r/d0f0db68-98b8-ebfb-16dc-f29df24cf012@google.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jue Wang <juew@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |   24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

--- a/mm/huge_memory.c~mm-thp-replace-debug_vm-bug-with-vm_warn-when-unmap-fails-for-split
+++ a/mm/huge_memory.c
@@ -2352,15 +2352,15 @@ static void unmap_page(struct page *page
 {
 	enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_SYNC |
 		TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
-	bool unmap_success;
 
 	VM_BUG_ON_PAGE(!PageHead(page), page);
 
 	if (PageAnon(page))
 		ttu_flags |= TTU_SPLIT_FREEZE;
 
-	unmap_success = try_to_unmap(page, ttu_flags);
-	VM_BUG_ON_PAGE(!unmap_success, page);
+	try_to_unmap(page, ttu_flags);
+
+	VM_WARN_ON_ONCE_PAGE(page_mapped(page), page);
 }
 
 static void remap_page(struct page *page, unsigned int nr)
@@ -2671,7 +2671,7 @@ int split_huge_page_to_list(struct page
 	struct deferred_split *ds_queue = get_deferred_split_queue(head);
 	struct anon_vma *anon_vma = NULL;
 	struct address_space *mapping = NULL;
-	int count, mapcount, extra_pins, ret;
+	int extra_pins, ret;
 	pgoff_t end;
 
 	VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
@@ -2730,7 +2730,6 @@ int split_huge_page_to_list(struct page
 	}
 
 	unmap_page(head);
-	VM_BUG_ON_PAGE(compound_mapcount(head), head);
 
 	/* block interrupt reentry in xa_lock and spinlock */
 	local_irq_disable();
@@ -2748,9 +2747,7 @@ int split_huge_page_to_list(struct page
 
 	/* Prevent deferred_split_scan() touching ->_refcount */
 	spin_lock(&ds_queue->split_queue_lock);
-	count = page_count(head);
-	mapcount = total_mapcount(head);
-	if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
+	if (page_ref_freeze(head, 1 + extra_pins)) {
 		if (!list_empty(page_deferred_list(head))) {
 			ds_queue->split_queue_len--;
 			list_del(page_deferred_list(head));
@@ -2770,16 +2767,9 @@ int split_huge_page_to_list(struct page
 		__split_huge_page(page, list, end);
 		ret = 0;
 	} else {
-		if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
-			pr_alert("total_mapcount: %u, page_count(): %u\n",
-					mapcount, count);
-			if (PageTail(page))
-				dump_page(head, NULL);
-			dump_page(page, "total_mapcount(head) > 0");
-			BUG();
-		}
 		spin_unlock(&ds_queue->split_queue_lock);
-fail:		if (mapping)
+fail:
+		if (mapping)
 			xa_unlock(&mapping->i_pages);
 		local_irq_enable();
 		remap_page(head, thp_nr_pages(head));
_

  parent reply	other threads:[~2021-06-16  1:24 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-16  1:22 incoming Andrew Morton
2021-06-16  1:23 ` [patch 01/18] mm,hwpoison: fix race with hugetlb page allocation Andrew Morton
2021-06-16  1:23 ` [patch 02/18] mm/swap: fix pte_same_as_swp() not removing uffd-wp bit when compare Andrew Morton
2021-06-16  1:23 ` [patch 03/18] mm/slub: clarify verification reporting Andrew Morton
2021-06-16  1:23 ` [patch 04/18] mm/slub: fix redzoning for small allocations Andrew Morton
2021-06-16  1:23 ` [patch 05/18] mm/slub: actually fix freelist pointer vs redzoning Andrew Morton
2021-06-16  1:23 ` [patch 06/18] mm/hugetlb: expand restore_reserve_on_error functionality Andrew Morton
2021-06-16  1:23 ` [patch 07/18] mm/memory-failure: make sure wait for page writeback in memory_failure Andrew Morton
2021-06-16  1:23 ` [patch 08/18] crash_core, vmcoreinfo: append 'SECTION_SIZE_BITS' to vmcoreinfo Andrew Morton
2021-06-16  1:23 ` [patch 09/18] mm/slub.c: include swab.h Andrew Morton
2021-06-16  1:23 ` [patch 10/18] mm, thp: use head page in __migration_entry_wait() Andrew Morton
2021-06-16  1:23 ` [patch 11/18] mm/thp: fix __split_huge_pmd_locked() on shmem migration entry Andrew Morton
2021-06-16  1:23 ` [patch 12/18] mm/thp: make is_huge_zero_pmd() safe and quicker Andrew Morton
2021-06-16  1:23 ` [patch 13/18] mm/thp: try_to_unmap() use TTU_SYNC for safe splitting Andrew Morton
2021-06-16  1:23 ` [patch 14/18] mm/thp: fix vma_address() if virtual address below file offset Andrew Morton
2021-06-16  1:24 ` [patch 15/18] mm/thp: fix page_address_in_vma() on file THP tails Andrew Morton
2021-06-16  1:24 ` [patch 16/18] mm/thp: unmap_mapping_page() to fix THP truncate_cleanup_page() Andrew Morton
2021-06-16  1:24 ` Andrew Morton [this message]
2021-06-16  1:24 ` [patch 18/18] mm/sparse: fix check_usemap_section_nr warnings Andrew Morton

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