linux-kernel - [PATCH] mm/mmap: refactor mlock_future

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Message-Id: <20230522082412.56685-1-lstoakes@gmail.com>
Date:   Mon, 22 May 2023 09:24:12 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Rapoport <rppt@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Lorenzo Stoakes <lstoakes@...il.com>
Subject: [PATCH] mm/mmap: refactor mlock_future_check()

In all but one instance, mlock_future_check() is treated as a boolean
function despite returning an error code. In one instance, this error code
is ignored and replaced with -ENOMEM.

This is confusing, and the inversion of true -> failure, false -> success
is not warranted. Convert the function to a bool, lightly refactor and
return true if the check passes, false if not.

Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
---
 mm/internal.h  |  4 ++--
 mm/mmap.c      | 33 +++++++++++++++++----------------
 mm/mremap.c    |  2 +-
 mm/secretmem.c |  2 +-
 4 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index bb6542279599..66dd214b302a 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -576,8 +576,8 @@ extern long populate_vma_page_range(struct vm_area_struct *vma,
 extern long faultin_vma_page_range(struct vm_area_struct *vma,
 				   unsigned long start, unsigned long end,
 				   bool write, int *locked);
-extern int mlock_future_check(struct mm_struct *mm, unsigned long flags,
-			      unsigned long len);
+extern bool mlock_future_check(struct mm_struct *mm, unsigned long flags,
+			       unsigned long bytes);
 /*
  * mlock_vma_folio() and munlock_vma_folio():
  * should be called with vma's mmap_lock held for read or write,
diff --git a/mm/mmap.c b/mm/mmap.c
index 877696464c09..10f2d5d689da 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -182,7 +182,8 @@ static int check_brk_limits(unsigned long addr, unsigned long len)
 	if (IS_ERR_VALUE(mapped_addr))
 		return mapped_addr;
 
-	return mlock_future_check(current->mm, current->mm->def_flags, len);
+	return mlock_future_check(current->mm, current->mm->def_flags, len)
+		? 0 : -EAGAIN;
 }
 static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *brkvma,
 		unsigned long addr, unsigned long request, unsigned long flags);
@@ -1148,21 +1149,21 @@ static inline unsigned long round_hint_to_min(unsigned long hint)
 	return hint;
 }
 
-int mlock_future_check(struct mm_struct *mm, unsigned long flags,
-		       unsigned long len)
+bool mlock_future_check(struct mm_struct *mm, unsigned long flags,
+			unsigned long bytes)
 {
-	unsigned long locked, lock_limit;
+	unsigned long locked_pages, limit_pages;
 
-	/*  mlock MCL_FUTURE? */
-	if (flags & VM_LOCKED) {
-		locked = len >> PAGE_SHIFT;
-		locked += mm->locked_vm;
-		lock_limit = rlimit(RLIMIT_MEMLOCK);
-		lock_limit >>= PAGE_SHIFT;
-		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
-			return -EAGAIN;
-	}
-	return 0;
+	if (!(flags & VM_LOCKED) || capable(CAP_IPC_LOCK))
+		return true;
+
+	locked_pages = bytes >> PAGE_SHIFT;
+	locked_pages += mm->locked_vm;
+
+	limit_pages = rlimit(RLIMIT_MEMLOCK);
+	limit_pages >>= PAGE_SHIFT;
+
+	return locked_pages <= limit_pages;
 }
 
 static inline u64 file_mmap_size_max(struct file *file, struct inode *inode)
@@ -1274,7 +1275,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 		if (!can_do_mlock())
 			return -EPERM;
 
-	if (mlock_future_check(mm, vm_flags, len))
+	if (!mlock_future_check(mm, vm_flags, len))
 		return -EAGAIN;
 
 	if (file) {
@@ -1926,7 +1927,7 @@ static int acct_stack_growth(struct vm_area_struct *vma,
 		return -ENOMEM;
 
 	/* mlock limit tests */
-	if (mlock_future_check(mm, vma->vm_flags, grow << PAGE_SHIFT))
+	if (!mlock_future_check(mm, vma->vm_flags, grow << PAGE_SHIFT))
 		return -ENOMEM;
 
 	/* Check to ensure the stack will not grow into a hugetlb-only region */
diff --git a/mm/mremap.c b/mm/mremap.c
index b11ce6c92099..bcfcb8df5875 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -775,7 +775,7 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
 	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 		return ERR_PTR(-EFAULT);
 
-	if (mlock_future_check(mm, vma->vm_flags, new_len - old_len))
+	if (!mlock_future_check(mm, vma->vm_flags, new_len - old_len))
 		return ERR_PTR(-EAGAIN);
 
 	if (!may_expand_vm(mm, vma->vm_flags,
diff --git a/mm/secretmem.c b/mm/secretmem.c
index 974b32ba8b9d..58d2af12df4f 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -125,7 +125,7 @@ static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
 	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
 		return -EINVAL;
 
-	if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
+	if (!mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
 		return -EAGAIN;
 
 	vm_flags_set(vma, VM_LOCKED | VM_DONTDUMP);
-- 
2.40.1