mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split
[ Upstream commit 504e070dc08f757bccaed6d05c0f53ecbfac8a23 ] 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 in split_huge_page_to_list(), and fixed up the conflict on ttu_flags in unmap_page(). Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -2462,15 +2462,15 @@ static void unmap_page(struct page *page)
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{
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{
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enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
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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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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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VM_BUG_ON_PAGE(!PageHead(page), page);
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if (PageAnon(page))
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if (PageAnon(page))
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ttu_flags |= TTU_SPLIT_FREEZE;
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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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try_to_unmap(page, ttu_flags);
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VM_BUG_ON_PAGE(!unmap_success, page);
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VM_WARN_ON_ONCE_PAGE(page_mapped(page), page);
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}
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}
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static void remap_page(struct page *page)
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static void remap_page(struct page *page)
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@ -2749,7 +2749,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
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struct deferred_split *ds_queue = get_deferred_split_queue(page);
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struct deferred_split *ds_queue = get_deferred_split_queue(page);
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struct anon_vma *anon_vma = NULL;
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struct anon_vma *anon_vma = NULL;
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struct address_space *mapping = 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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bool mlocked;
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unsigned long flags;
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unsigned long flags;
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pgoff_t end;
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pgoff_t end;
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@ -2811,7 +2811,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
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mlocked = PageMlocked(page);
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mlocked = PageMlocked(page);
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unmap_page(head);
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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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/* Make sure the page is not on per-CPU pagevec as it takes pin */
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if (mlocked)
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if (mlocked)
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@ -2834,9 +2833,7 @@ 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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/* Prevent deferred_split_scan() touching ->_refcount */
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spin_lock(&ds_queue->split_queue_lock);
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spin_lock(&ds_queue->split_queue_lock);
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count = page_count(head);
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if (page_ref_freeze(head, 1 + extra_pins)) {
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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 (!list_empty(page_deferred_list(head))) {
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if (!list_empty(page_deferred_list(head))) {
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ds_queue->split_queue_len--;
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ds_queue->split_queue_len--;
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list_del(page_deferred_list(head));
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list_del(page_deferred_list(head));
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@ -2857,16 +2854,9 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
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} else
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} else
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ret = 0;
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ret = 0;
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} else {
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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(&ds_queue->split_queue_lock);
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spin_unlock(&ds_queue->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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xa_unlock(&mapping->i_pages);
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xa_unlock(&mapping->i_pages);
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spin_unlock_irqrestore(&pgdata->lru_lock, flags);
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spin_unlock_irqrestore(&pgdata->lru_lock, flags);
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remap_page(head);
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remap_page(head);
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