mm/migrate: avoid possible unnecessary process right check in kernel_move_pages()
There is no need to check if this process has the right to modify the
specified process when they are same. And we could also skip the security
hook call if a process is modifying its own pages. Add helper function to
handle these.
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Hongxiang Lou <louhongxiang@huawei.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christopher Lameter <cl@linux.com>
Link: https://lkml.kernel.org/r/20200819083331.19012-1-linmiaohe@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/migrate.c b/mm/migrate.c
index 4cf1af8..5ca5842 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1864,6 +1864,53 @@
return nr_pages ? -EFAULT : 0;
}
+static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes)
+{
+ struct task_struct *task;
+ struct mm_struct *mm;
+
+ /*
+ * There is no need to check if current process has the right to modify
+ * the specified process when they are same.
+ */
+ if (!pid) {
+ mmget(current->mm);
+ *mem_nodes = cpuset_mems_allowed(current);
+ return current->mm;
+ }
+
+ /* Find the mm_struct */
+ rcu_read_lock();
+ task = find_task_by_vpid(pid);
+ if (!task) {
+ rcu_read_unlock();
+ return ERR_PTR(-ESRCH);
+ }
+ get_task_struct(task);
+
+ /*
+ * Check if this process has the right to modify the specified
+ * process. Use the regular "ptrace_may_access()" checks.
+ */
+ if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
+ rcu_read_unlock();
+ mm = ERR_PTR(-EPERM);
+ goto out;
+ }
+ rcu_read_unlock();
+
+ mm = ERR_PTR(security_task_movememory(task));
+ if (IS_ERR(mm))
+ goto out;
+ *mem_nodes = cpuset_mems_allowed(task);
+ mm = get_task_mm(task);
+out:
+ put_task_struct(task);
+ if (!mm)
+ mm = ERR_PTR(-EINVAL);
+ return mm;
+}
+
/*
* Move a list of pages in the address space of the currently executing
* process.
@@ -1873,7 +1920,6 @@
const int __user *nodes,
int __user *status, int flags)
{
- struct task_struct *task;
struct mm_struct *mm;
int err;
nodemask_t task_nodes;
@@ -1885,36 +1931,9 @@
if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
return -EPERM;
- /* Find the mm_struct */
- rcu_read_lock();
- task = pid ? find_task_by_vpid(pid) : current;
- if (!task) {
- rcu_read_unlock();
- return -ESRCH;
- }
- get_task_struct(task);
-
- /*
- * Check if this process has the right to modify the specified
- * process. Use the regular "ptrace_may_access()" checks.
- */
- if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
- rcu_read_unlock();
- err = -EPERM;
- goto out;
- }
- rcu_read_unlock();
-
- err = security_task_movememory(task);
- if (err)
- goto out;
-
- task_nodes = cpuset_mems_allowed(task);
- mm = get_task_mm(task);
- put_task_struct(task);
-
- if (!mm)
- return -EINVAL;
+ mm = find_mm_struct(pid, &task_nodes);
+ if (IS_ERR(mm))
+ return PTR_ERR(mm);
if (nodes)
err = do_pages_move(mm, task_nodes, nr_pages, pages,
@@ -1924,10 +1943,6 @@
mmput(mm);
return err;
-
-out:
- put_task_struct(task);
- return err;
}
SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
