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authorLi Xinhai <lixinhai.lxh@gmail.com>2022-01-14 23:05:16 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2022-01-15 15:30:26 +0100
commit28b0ee3fb35047bd2bac57cc5a051b26bbd9b194 (patch)
treed309b4c6ef49c4223414b88801e010642141f080 /mm/gup.c
parentgup: avoid multiple user access locking/unlocking in fault_in_{read/write}able (diff)
downloadlinux-28b0ee3fb35047bd2bac57cc5a051b26bbd9b194.tar.xz
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mm/gup.c: stricter check on THP migration entry during follow_pmd_mask
When BUG_ON check for THP migration entry, the existing code only check thp_migration_supported case, but not for !thp_migration_supported case. If !thp_migration_supported() and !pmd_present(), the original code may dead loop in theory. To make the BUG_ON check consistent, we need catch both cases. Move the BUG_ON check one step earlier, because if the bug happen we should know it instead of depend on FOLL_MIGRATION been used by caller. Because pmdval instead of *pmd is read by the is_pmd_migration_entry() check, the existing code don't help to avoid useless locking within pmd_migration_entry_wait(), so remove that check. Link: https://lkml.kernel.org/r/20211217062559.737063-1-lixinhai.lxh@gmail.com Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com> Cc: Zi Yan <ziy@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/gup.c')
-rw-r--r--mm/gup.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/mm/gup.c b/mm/gup.c
index be2a41feec7d..f0af462ac1e2 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -642,12 +642,17 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
}
retry:
if (!pmd_present(pmdval)) {
+ /*
+ * Should never reach here, if thp migration is not supported;
+ * Otherwise, it must be a thp migration entry.
+ */
+ VM_BUG_ON(!thp_migration_supported() ||
+ !is_pmd_migration_entry(pmdval));
+
if (likely(!(flags & FOLL_MIGRATION)))
return no_page_table(vma, flags);
- VM_BUG_ON(thp_migration_supported() &&
- !is_pmd_migration_entry(pmdval));
- if (is_pmd_migration_entry(pmdval))
- pmd_migration_entry_wait(mm, pmd);
+
+ pmd_migration_entry_wait(mm, pmd);
pmdval = READ_ONCE(*pmd);
/*
* MADV_DONTNEED may convert the pmd to null because