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| author | Yang Shi <shy828301@gmail.com> | 2021-05-14 10:39:52 +1000 |
|---|---|---|
| committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2021-05-14 10:39:52 +1000 |
| commit | 69cc52577e67f437b4faaa2024faa279fabd2904 (patch) | |
| tree | b1975ffc433c79c3deedd10e4182c0e962f8a2b6 | |
| parent | 248470b9914c9df4504eb1328b8c8e4a9aeb295b (diff) | |
| download | linux-next-69cc52577e67f437b4faaa2024faa279fabd2904.tar.gz | |
mm: thp: check total_mapcount instead of page_mapcount
Notice: this object is not reachable from any branch.
When debugging the bug reported by Wang Yugui [1], try_to_unmap() may
return false positive for PTE-mapped THP since page_mapcount() is used to
check if the THP is unmapped, but it just checks compound mapcount and
head page's mapcount. If the THP is PTE-mapped and head page is not
mapped, it may return a false positive.
Use total_mapcount() instead of page_mapcount() for try_to_unmap() and do
so for the VM_BUG_ON_PAGE in split_huge_page_to_list as well.
This changes the semantics of try_to_unmap(), but I don't see there is any
use case that expects try_to_unmap() to just unmap one subpage of a huge
page. So using page_mapcount() seems like a bug.
[1] https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/
Link: https://lkml.kernel.org/r/20210513212334.217424-1-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Notice: this object is not reachable from any branch.
| -rw-r--r-- | mm/huge_memory.c | 11 | ||||
| -rw-r--r-- | mm/rmap.c | 10 |
2 files changed, 7 insertions, 14 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index f1fad87472859..52ca04b905cf2 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2350,7 +2350,6 @@ static void unmap_page(struct page *page) ttu_flags |= TTU_SPLIT_FREEZE; unmap_success = try_to_unmap(page, ttu_flags); - VM_BUG_ON_PAGE(!unmap_success, page); } static void remap_page(struct page *page, unsigned int nr) @@ -2720,7 +2719,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) } unmap_page(head); - VM_BUG_ON_PAGE(compound_mapcount(head), head); + VM_BUG_ON_PAGE(total_mapcount(head), head); /* block interrupt reentry in xa_lock and spinlock */ local_irq_disable(); @@ -2760,14 +2759,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) __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) xa_unlock(&mapping->i_pages); diff --git a/mm/rmap.c b/mm/rmap.c index 693a610e181d1..f52825b1330d8 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1742,12 +1742,14 @@ static int page_not_mapped(struct page *page) } /** - * try_to_unmap - try to remove all page table mappings to a page - * @page: the page to get unmapped + * try_to_unmap - try to remove all page table mappings to a page and the + * compound page it belongs to + * @page: the page or the subpages of compound page to get unmapped * @flags: action and flags * * Tries to remove all the page table entries which are mapping this - * page, used in the pageout path. Caller must hold the page lock. + * page and the compound page it belongs to, used in the pageout path. + * Caller must hold the page lock. * * If unmap is successful, return true. Otherwise, false. */ @@ -1777,7 +1779,7 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags) else rmap_walk(page, &rwc); - return !page_mapcount(page) ? true : false; + return !total_mapcount(page) ? true : false; } /** |