[PATCH v5 09/10] mmap locking API: add mmap_assert_locked

[Michel Lespinasse <walken@xxxxxxxxxx>]

Add mmap_assert_locked to assert that mmap_sem is held.

Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
---
 fs/userfaultfd.c          |  6 +++---
 include/linux/mmap_lock.h | 10 ++++++++++
 mm/gup.c                  |  2 +-
 mm/memory.c               |  2 +-
 4 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 9c645eee1a59..12b492409040 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -234,7 +234,7 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
 	pte_t *ptep, pte;
 	bool ret = true;
 
-	VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
+	mmap_assert_locked(mm);
 
 	ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
 
@@ -286,7 +286,7 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
 	pte_t *pte;
 	bool ret = true;
 
-	VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
+	mmap_assert_locked(mm);
 
 	pgd = pgd_offset(mm, address);
 	if (!pgd_present(*pgd))
@@ -405,7 +405,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	 * Coredumping runs without mmap_sem so we can only check that
 	 * the mmap_sem is held, if PF_DUMPCORE was not set.
 	 */
-	WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
+	mmap_assert_locked(mm);
 
 	ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
 	if (!ctx)
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 9e104835a0d1..f7a3a9550cc5 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -1,6 +1,8 @@
 #ifndef _LINUX_MMAP_LOCK_H
 #define _LINUX_MMAP_LOCK_H
 
+#include <linux/mmdebug.h>
+
 #define MMAP_LOCK_INITIALIZER(name) \
 	.mmap_sem = __RWSEM_INITIALIZER(name.mmap_sem),
 
@@ -73,4 +75,12 @@ static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
 	up_read_non_owner(&mm->mmap_sem);
 }
 
+static inline void mmap_assert_locked(struct mm_struct *mm)
+{
+	if (IS_ENABLED(CONFIG_LOCKDEP) && debug_locks)
+		VM_BUG_ON_MM(!lockdep_is_held(&mm->mmap_sem), mm);
+	else
+		VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
+}
+
 #endif /* _LINUX_MMAP_LOCK_H */
diff --git a/mm/gup.c b/mm/gup.c
index 0404e52513b2..e12993ceb711 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1403,7 +1403,7 @@ long populate_vma_page_range(struct vm_area_struct *vma,
 	VM_BUG_ON(end   & ~PAGE_MASK);
 	VM_BUG_ON_VMA(start < vma->vm_start, vma);
 	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
-	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
+	mmap_assert_locked(mm);
 
 	gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;
 	if (vma->vm_flags & VM_LOCKONFAULT)
diff --git a/mm/memory.c b/mm/memory.c
index e6dd3309c5a3..20f98ea8968e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1214,7 +1214,7 @@ static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
 		next = pud_addr_end(addr, end);
 		if (pud_trans_huge(*pud) || pud_devmap(*pud)) {
 			if (next - addr != HPAGE_PUD_SIZE) {
-				VM_BUG_ON_VMA(!rwsem_is_locked(&tlb->mm->mmap_sem), vma);
+				mmap_assert_locked(tlb->mm);
 				split_huge_pud(vma, pud, addr);
 			} else if (zap_huge_pud(tlb, vma, pud, addr))
 				goto next;
-- 
2.26.1.301.g55bc3eb7cb9-goog