The patch titled
Subject: mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split
has been added to the -mm tree. Its filename is
mm-thp-replace-debug_vm-bug-with-vm_warn-when-unmap-fails-for-split.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-replace-debug_vm-bug-with-vm_warn-when-unmap-fails-for-split.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-replace-debug_vm-bug-with-vm_warn-when-unmap-fails-for-split.patch
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------------------------------------------------------
From: Yang Shi <shy828301@xxxxxxxxx>
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-tec=
h.com/
Link: https://lkml.kernel.org/r/20210526201239.3351-1-shy828301@xxxxxxxxx
Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 29 +++++++++--------------------
1 file changed, 9 insertions(+), 20 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
@@ -2300,21 +2300,20 @@ void vma_adjust_trans_huge(struct vm_are
static void unmap_page(struct page *page)
{
enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
- bool unmap_success;
VM_BUG_ON_PAGE(!PageHead(page), page);
- if (PageAnon(page))
+ if (PageAnon(page)) {
try_to_migrate(page, ttu_flags);
- else
+ } else {
/*
* Don't install migration entries for file backed pages. This
* helps handle cases when i_size is in the middle of the page
* as there is no need to unmap pages beyond i_size manually.
*/
- unmap_success = try_to_unmap(page, ttu_flags |
- TTU_IGNORE_MLOCK);
- VM_BUG_ON_PAGE(!unmap_success, page);
+ try_to_unmap(page, ttu_flags | TTU_IGNORE_MLOCK);
+ }
+ VM_WARN_ON_ONCE_PAGE(page_mapped(page), page);
}
static void remap_page(struct page *page, unsigned int nr)
@@ -2625,7 +2624,7 @@ 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);
@@ -2684,7 +2683,6 @@ 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();
@@ -2702,9 +2700,7 @@ 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));
@@ -2724,16 +2720,9 @@ 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));
_
Patches currently in -mm which might be from shy828301@xxxxxxxxx are
mm-memory-add-orig_pmd-to-struct-vm_fault.patch
mm-memory-make-numa_migrate_prep-non-static.patch
mm-thp-refactor-numa-fault-handling.patch
mm-migrate-account-thp-numa-migration-counters-correctly.patch
mm-migrate-dont-split-thp-for-misplaced-numa-page.patch
mm-migrate-check-mapcount-for-thp-instead-of-refcount.patch
mm-thp-skip-make-pmd-prot_none-if-thp-migration-is-not-supported.patch
mm-thp-replace-debug_vm-bug-with-vm_warn-when-unmap-fails-for-split.patch
mm-rmap-make-try_to_unmap-void-function.patch
