commit 00f89d218523b9bf6b522349c039d5ac80aa536d
author Oleg Nesterov <oleg@redhat.com> Fri Jul 10 03:27:38 2009 +0200
committer James Morris <jmorris@namei.org> Mon Aug 10 20:48:32 2009 +1000
tree cde7a8bde2798e4fb3ae28756f6cedd4db9191cc
parent 13f0feafa6b8aead57a2a328e2fca6a5828bf286

mm_for_maps: shift down_read(mmap_sem) to the caller

mm_for_maps() takes ->mmap_sem after security checks, this looks
strange and obfuscates the locking rules. Move this lock to its
single caller, m_start().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

fs/proc/base.c

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 917f338..f3c2e40 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -235,9 +235,8 @@
 struct mm_struct *mm_for_maps(struct task_struct *task)
 {
 	struct mm_struct *mm = get_task_mm(task);
-	if (!mm)
-		return NULL;
-	if (mm != current->mm) {
+
+	if (mm && mm != current->mm) {
 		/*
 		 * task->mm can be changed before security check,
 		 * in that case we must notice the change after.
@@ -245,10 +244,9 @@
 		if (!ptrace_may_access(task, PTRACE_MODE_READ) ||
 		    mm != task->mm) {
 			mmput(mm);
-			return NULL;
+			mm = NULL;
 		}
 	}
-	down_read(&mm->mmap_sem);
 	return mm;
 }
 

fs/proc/task_mmu.c

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 6f61b7c..9bd8be1 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -119,6 +119,7 @@
 	mm = mm_for_maps(priv->task);
 	if (!mm)
 		return NULL;
+	down_read(&mm->mmap_sem);
 
 	tail_vma = get_gate_vma(priv->task);
 	priv->tail_vma = tail_vma;

fs/proc/task_nommu.c

diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 64a72e2..8f5c05d 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -189,6 +189,7 @@
 		priv->task = NULL;
 		return NULL;
 	}
+	down_read(&mm->mmap_sem);
 
 	/* start from the Nth VMA */
 	for (p = rb_first(&mm->mm_rb); p; p = rb_next(p))