[RFC PATCH 22/24] do_mmap: implement locked argument

[Michel Lespinasse <walken@google.com>]

When locked is true, preserve the current behavior - the do_mmap()
caller is expected to already hold a coarse write lock on current->mmap_sem

When locked is false, change do_mmap() to acquiring the appropriate
MM locks. do_mmap() still acquires a coarse lock in this change, but can
now be locally changed to acquire a fine grained lock in the future.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
 mm/mmap.c  | 106 ++++++++++++++++++++++++++++++++++++-----------------
 mm/nommu.c |  19 +++++++++-
 2 files changed, 89 insertions(+), 36 deletions(-)

diff --git mm/mmap.c mm/mmap.c
index 2868e61927a1..75755f1cbd0b 100644
--- mm/mmap.c
+++ mm/mmap.c
@@ -1406,22 +1406,29 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
 		return -EOVERFLOW;
 
+	if (!locked && mm_write_lock_killable(mm))
+		return -EINTR;
+
 	/* Too many mappings? */
-	if (mm->map_count > sysctl_max_map_count)
-		return -ENOMEM;
+	if (mm->map_count > sysctl_max_map_count) {
+		addr = -ENOMEM;
+		goto unlock;
+	}
 
 	/* Obtain the address to map to. we verify (or select) it and ensure
 	 * that it represents a valid section of the address space.
 	 */
 	addr = get_unmapped_area(file, addr, len, pgoff, flags);
 	if (IS_ERR_VALUE(addr))
-		return addr;
+		goto unlock;
 
 	if (flags & MAP_FIXED_NOREPLACE) {
 		struct vm_area_struct *vma = find_vma(mm, addr);
 
-		if (vma && vma->vm_start < addr + len)
-			return -EEXIST;
+		if (vma && vma->vm_start < addr + len) {
+			addr = -EEXIST;
+			goto unlock;
+		}
 	}
 
 	if (prot == PROT_EXEC) {
@@ -1437,19 +1444,24 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 	vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
 			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
 
-	if (flags & MAP_LOCKED)
-		if (!can_do_mlock())
-			return -EPERM;
+	if ((flags & MAP_LOCKED) && !can_do_mlock()) {
+		addr = -EPERM;
+		goto unlock;
+	}
 
-	if (mlock_future_check(mm, vm_flags, len))
-		return -EAGAIN;
+	if (mlock_future_check(mm, vm_flags, len)) {
+		addr = -EAGAIN;
+		goto unlock;
+	}
 
 	if (file) {
 		struct inode *inode = file_inode(file);
 		unsigned long flags_mask;
 
-		if (!file_mmap_ok(file, inode, pgoff, len))
-			return -EOVERFLOW;
+		if (!file_mmap_ok(file, inode, pgoff, len)) {
+			addr = -EOVERFLOW;
+			goto unlock;
+		}
 
 		flags_mask = LEGACY_MAP_MASK | file->f_op->mmap_supported_flags;
 
@@ -1465,27 +1477,37 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 			flags &= LEGACY_MAP_MASK;
 			/* fall through */
 		case MAP_SHARED_VALIDATE:
-			if (flags & ~flags_mask)
-				return -EOPNOTSUPP;
+			if (flags & ~flags_mask) {
+				addr = -EOPNOTSUPP;
+				goto unlock;
+			}
 			if (prot & PROT_WRITE) {
-				if (!(file->f_mode & FMODE_WRITE))
-					return -EACCES;
-				if (IS_SWAPFILE(file->f_mapping->host))
-					return -ETXTBSY;
+				if (!(file->f_mode & FMODE_WRITE)) {
+					addr = -EACCES;
+					goto unlock;
+				}
+				if (IS_SWAPFILE(file->f_mapping->host)) {
+					addr = -ETXTBSY;
+					goto unlock;
+				}
 			}
 
 			/*
 			 * Make sure we don't allow writing to an append-only
 			 * file..
 			 */
-			if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
-				return -EACCES;
+			if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE)) {
+				addr = -EACCES;
+				goto unlock;
+			}
 
 			/*
 			 * Make sure there are no mandatory locks on the file.
 			 */
-			if (locks_verify_locked(file))
-				return -EAGAIN;
+			if (locks_verify_locked(file)) {
+				addr = -EAGAIN;
+				goto unlock;
+			}
 
 			vm_flags |= VM_SHARED | VM_MAYSHARE;
 			if (!(file->f_mode & FMODE_WRITE))
@@ -1493,28 +1515,39 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 
 			/* fall through */
 		case MAP_PRIVATE:
-			if (!(file->f_mode & FMODE_READ))
-				return -EACCES;
+			if (!(file->f_mode & FMODE_READ)) {
+				addr = -EACCES;
+				goto unlock;
+			}
 			if (path_noexec(&file->f_path)) {
-				if (vm_flags & VM_EXEC)
-					return -EPERM;
+				if (vm_flags & VM_EXEC) {
+					addr = -EPERM;
+					goto unlock;
+				}
 				vm_flags &= ~VM_MAYEXEC;
 			}
 
-			if (!file->f_op->mmap)
-				return -ENODEV;
-			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
-				return -EINVAL;
+			if (!file->f_op->mmap) {
+				addr = -ENODEV;
+				goto unlock;
+			}
+			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP)) {
+				addr = -EINVAL;
+				goto unlock;
+			}
 			break;
 
 		default:
-			return -EINVAL;
+			addr = -EINVAL;
+			goto unlock;
 		}
 	} else {
 		switch (flags & MAP_TYPE) {
 		case MAP_SHARED:
-			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
-				return -EINVAL;
+			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP)) {
+				addr = -EINVAL;
+				goto unlock;
+			}
 			/*
 			 * Ignore pgoff.
 			 */
@@ -1528,7 +1561,8 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 			pgoff = addr >> PAGE_SHIFT;
 			break;
 		default:
-			return -EINVAL;
+			addr = -EINVAL;
+			goto unlock;
 		}
 	}
 
@@ -1551,6 +1585,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 	    ((vm_flags & VM_LOCKED) ||
 	     (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
 		*populate = len;
+
+unlock:
+	if (!locked)
+		mm_write_unlock(mm);
 	return addr;
 }
 
diff --git mm/nommu.c mm/nommu.c
index a2c2bf8d7676..7fb1db89d4f8 100644
--- mm/nommu.c
+++ mm/nommu.c
@@ -1107,6 +1107,7 @@ unsigned long do_mmap(struct file *file,
 			unsigned long *populate,
 			struct list_head *uf)
 {
+	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
 	struct vm_region *region;
 	struct rb_node *rb;
@@ -1115,12 +1116,18 @@ unsigned long do_mmap(struct file *file,
 
 	*populate = 0;
 
+	if (!locked && mm_write_lock_killable(mm))
+		return -EINTR;
+
 	/* decide whether we should attempt the mapping, and if so what sort of
 	 * mapping */
 	ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,
 				    &capabilities);
-	if (ret < 0)
+	if (ret < 0) {
+		if (!locked)
+			mm_write_unlock(mm);
 		return ret;
+	}
 
 	/* we ignore the address hint */
 	addr = 0;
@@ -1135,7 +1142,7 @@ unsigned long do_mmap(struct file *file,
 	if (!region)
 		goto error_getting_region;
 
-	vma = vm_area_alloc(current->mm);
+	vma = vm_area_alloc(mm);
 	if (!vma)
 		goto error_getting_vma;
 
@@ -1289,6 +1296,8 @@ unsigned long do_mmap(struct file *file,
 	}
 
 	up_write(&nommu_region_sem);
+	if (!locked)
+		mm_write_unlock(mm);
 
 	return result;
 
@@ -1301,6 +1310,8 @@ unsigned long do_mmap(struct file *file,
 	if (vma->vm_file)
 		fput(vma->vm_file);
 	vm_area_free(vma);
+	if (!locked)
+		mm_write_unlock(mm);
 	return ret;
 
 sharing_violation:
@@ -1314,12 +1325,16 @@ unsigned long do_mmap(struct file *file,
 	pr_warn("Allocation of vma for %lu byte allocation from process %d failed\n",
 			len, current->pid);
 	show_free_areas(0, NULL);
+	if (!locked)
+		mm_write_unlock(mm);
 	return -ENOMEM;
 
 error_getting_region:
 	pr_warn("Allocation of vm region for %lu byte allocation from process %d failed\n",
 			len, current->pid);
 	show_free_areas(0, NULL);
+	if (!locked)
+		mm_write_unlock(mm);
 	return -ENOMEM;
 }
 
-- 
2.25.0.341.g760bfbb309-goog