linux-kernel - [PATCH v5 1/8] mm: Remove BUG_ON mmap_sem not held from xxx_trans_huge

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Date:   Thu, 10 Oct 2019 14:43:07 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        torvalds@...ux-foundation.org, kirill@...temov.name
Cc:     Thomas Hellstrom <thellstrom@...are.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>
Subject: [PATCH v5 1/8] mm: Remove BUG_ON mmap_sem not held from xxx_trans_huge_lock()

From: Thomas Hellstrom <thellstrom@...are.com>

The caller needs to make sure that the vma is not torn down during the
lock operation and can also use the i_mmap_rwsem for file-backed vmas.
Remove the BUG_ON. We could, as an alternative, add a test that either
vma->vm_mm->mmap_sem or vma->vm_file->f_mapping->i_mmap_rwsem are held.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Will Deacon <will.deacon@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Huang Ying <ying.huang@...el.com>
Cc: Jérôme Glisse <jglisse@...hat.com>
Cc: Kirill A. Shutemov <kirill@...temov.name>
Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
Acked-by: Kirill A. Shutemov <kirill@...temov.name>
---
 include/linux/huge_mm.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 93d5cf0bc716..0b84e13e88e2 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -216,7 +216,6 @@ static inline int is_swap_pmd(pmd_t pmd)
 static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd,
 		struct vm_area_struct *vma)
 {
-	VM_BUG_ON_VMA(!rwsem_is_locked(&vma->vm_mm->mmap_sem), vma);
 	if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd))
 		return __pmd_trans_huge_lock(pmd, vma);
 	else
@@ -225,7 +224,6 @@ static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd,
 static inline spinlock_t *pud_trans_huge_lock(pud_t *pud,
 		struct vm_area_struct *vma)
 {
-	VM_BUG_ON_VMA(!rwsem_is_locked(&vma->vm_mm->mmap_sem), vma);
 	if (pud_trans_huge(*pud) || pud_devmap(*pud))
 		return __pud_trans_huge_lock(pud, vma);
 	else
-- 
2.21.0