From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Yang Shi <shy828301@gmail.com>,
Wang Yugui <wangyugui@e16-tech.com>,
Matthew Wilcox <willy@infradead.org>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
Alistair Popple <apopple@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>, Zi Yan <ziy@nvidia.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Minchan Kim <minchan@kernel.org>, Jue Wang <juew@google.com>,
Peter Xu <peterx@redhat.com>, Jan Kara <jack@suse.cz>,
Shakeel Butt <shakeelb@google.com>,
Oscar Salvador <osalvador@suse.de>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 07/10] mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split
Date: Tue, 8 Jun 2021 21:22:39 -0700 (PDT) [thread overview]
Message-ID: <d0f0db68-98b8-ebfb-16dc-f29df24cf012@google.com> (raw)
In-Reply-To: <af88612-1473-2eaa-903-8d1a448b26@google.com>
From: Yang Shi <shy828301@gmail.com>
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/
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: <stable@vger.kernel.org>
---
Patch inserted since the v1 series was posted.
v5: Rediffed by Hugh to fit after 6/7 in his mm/thp series; Cc stable.
v4: Updated the subject and commit log per Hugh.
Reordered the patches per Hugh.
v3: Incorporated the comments from Hugh. Keep Zi Yan's reviewed-by tag
since there is no fundamental change against v2.
v2: Removed dead code and updated the comment of try_to_unmap() per Zi
Yan.
mm/huge_memory.c | 24 +++++++-----------------
1 file changed, 7 insertions(+), 17 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 84ab735139dc..6d2a0119fc58 100644
--- a/mm/huge_memory.c
+++ b/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 *page, struct list_head *list)
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 *page, struct list_head *list)
}
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 *page, struct list_head *list)
/* 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 *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)
+fail:
+ if (mapping)
xa_unlock(&mapping->i_pages);
local_irq_enable();
remap_page(head, thp_nr_pages(head));
--
2.26.2
next prev parent reply other threads:[~2021-06-09 4:22 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <af88612-1473-2eaa-903-8d1a448b26@google.com>
2021-06-09 4:08 ` [PATCH v2 02/10] mm/thp: make is_huge_zero_pmd() safe and quicker Hugh Dickins
2021-06-09 10:22 ` Kirill A. Shutemov
2021-06-09 16:56 ` Yang Shi
2021-06-09 4:14 ` [PATCH v2 04/10] mm/thp: fix vma_address() if virtual address below file offset Hugh Dickins
2021-06-09 4:16 ` [PATCH v2 05/10] mm/thp: fix page_address_in_vma() on file THP tails Hugh Dickins
2021-06-09 4:19 ` [PATCH v2 06/10] mm/thp: unmap_mapping_page() to fix THP truncate_cleanup_page() Hugh Dickins
2021-06-09 17:02 ` Yang Shi
2021-06-09 21:11 ` Hugh Dickins
2021-06-09 21:16 ` [PATCH v3 " Hugh Dickins
2021-06-09 21:51 ` Yang Shi
2021-06-09 4:22 ` Hugh Dickins [this message]
2021-06-09 4:25 ` [PATCH v2 08/10] mm: rmap: make try_to_unmap() void function Hugh Dickins
2021-06-10 7:57 ` HORIGUCHI NAOYA(堀口 直也)
2021-06-09 4:27 ` [PATCH v2 09/10] mm/thp: remap_page() is only needed on anonymous THP Hugh Dickins
2021-06-09 4:30 ` [PATCH v2 10/10] mm: hwpoison_user_mappings() try_to_unmap() with TTU_SYNC Hugh Dickins
2021-06-09 10:27 ` Kirill A. Shutemov
2021-06-10 7:38 ` HORIGUCHI NAOYA(堀口 直也)
[not found] ` <20210610151505.d0124033e55bda07fa3d4408@linux-foundation.org>
[not found] ` <2014832.e7zRqyNrDn@nvdebian>
2021-06-11 0:15 ` [PATCH v2 00/10] mm/thp: fix THP splitting unmap BUGs and related Hugh Dickins
2021-06-11 7:28 ` Alistair Popple
2021-06-11 20:56 ` Hugh Dickins
2021-06-12 7:34 ` Alistair Popple
2021-06-12 8:20 ` Hugh Dickins
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