mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split
[ Upstream commit 504e070dc0
]
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.
As 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Note on stable backport: fixed up variables, split_queue_lock, tree_lock
in split_huge_page_to_list(), and conflict on ttu_flags in unmap_page().
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
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@ -2325,15 +2325,15 @@ static void unmap_page(struct page *page)
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{
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enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
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TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD | TTU_SYNC;
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bool unmap_success;
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VM_BUG_ON_PAGE(!PageHead(page), page);
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if (PageAnon(page))
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ttu_flags |= TTU_SPLIT_FREEZE;
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unmap_success = try_to_unmap(page, ttu_flags);
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VM_BUG_ON_PAGE(!unmap_success, page);
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try_to_unmap(page, ttu_flags);
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VM_WARN_ON_ONCE_PAGE(page_mapped(page), page);
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}
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static void remap_page(struct page *page)
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@ -2586,7 +2586,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
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struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
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struct anon_vma *anon_vma = NULL;
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struct address_space *mapping = NULL;
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int count, mapcount, extra_pins, ret;
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int extra_pins, ret;
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bool mlocked;
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unsigned long flags;
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pgoff_t end;
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@ -2648,7 +2648,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
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mlocked = PageMlocked(page);
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unmap_page(head);
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VM_BUG_ON_PAGE(compound_mapcount(head), head);
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/* Make sure the page is not on per-CPU pagevec as it takes pin */
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if (mlocked)
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@ -2674,9 +2673,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
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/* Prevent deferred_split_scan() touching ->_refcount */
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spin_lock(&pgdata->split_queue_lock);
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count = page_count(head);
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mapcount = total_mapcount(head);
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if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
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if (page_ref_freeze(head, 1 + extra_pins)) {
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if (!list_empty(page_deferred_list(head))) {
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pgdata->split_queue_len--;
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list_del(page_deferred_list(head));
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@ -2692,16 +2689,9 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
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} else
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ret = 0;
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} else {
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if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
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pr_alert("total_mapcount: %u, page_count(): %u\n",
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mapcount, count);
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if (PageTail(page))
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dump_page(head, NULL);
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dump_page(page, "total_mapcount(head) > 0");
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BUG();
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}
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spin_unlock(&pgdata->split_queue_lock);
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fail: if (mapping)
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fail:
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if (mapping)
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spin_unlock(&mapping->tree_lock);
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spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
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remap_page(head);
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