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authorOleg Nesterov <oleg@redhat.com>2009-07-16 19:09:36 -0400
committerJames Morris <jmorris@namei.org>2009-07-16 19:09:36 -0400
commitd2e3ee9b29f5de5b01e611b04e6fb29760589b01 (patch)
treead73b17c2c6b83050a948685a0a3af3f907de67f /lib
parent713c0ecdb888e9ef6f085e828555455c5916b07f (diff)
kernel: fix is_single_threaded
- Fix the comment, is_single_threaded(p) actually means that nobody shares ->mm with p. I think this helper should be renamed, and it should not have arguments. With or without this patch it must not be used unless p == current, otherwise we can't safely use p->signal or p->mm. - "if (atomic_read(&p->signal->count) != 1)" is not right when we have a zombie group leader, use signal->live instead. - Add PF_KTHREAD check to skip kernel threads which may borrow p->mm, otherwise we can return the wrong "false". - Use for_each_process() instead of do_each_thread(), all threads must use the same ->mm. - Use down_write(mm->mmap_sem) + rcu_read_lock() instead of tasklist_lock to iterate over the process list. If there is another CLONE_VM process it can't pass exit_mm() which takes the same mm->mmap_sem. We can miss a freshly forked CLONE_VM task, but this doesn't matter because we must see its parent and return false. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: James Morris <jmorris@namei.org> Cc: Roland McGrath <roland@redhat.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/is_single_threaded.c62
1 files changed, 36 insertions, 26 deletions
diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
index f1ed2fe76c65..2762516e0a5e 100644
--- a/lib/is_single_threaded.c
+++ b/lib/is_single_threaded.c
@@ -12,34 +12,44 @@
12 12
13#include <linux/sched.h> 13#include <linux/sched.h>
14 14
15/** 15/*
16 * is_single_threaded - Determine if a thread group is single-threaded or not 16 * Returns true if the task does not share ->mm with another thread/process.
17 * @p: A task in the thread group in question
18 *
19 * This returns true if the thread group to which a task belongs is single
20 * threaded, false if it is not.
21 */ 17 */
22bool is_single_threaded(struct task_struct *p) 18bool is_single_threaded(struct task_struct *task)
23{ 19{
24 struct task_struct *g, *t; 20 struct mm_struct *mm = task->mm;
25 struct mm_struct *mm = p->mm; 21 struct task_struct *p, *t;
26 22 bool ret;
27 if (atomic_read(&p->signal->count) != 1) 23
28 goto no; 24 might_sleep();
29 25
30 if (atomic_read(&p->mm->mm_users) != 1) { 26 if (atomic_read(&task->signal->live) != 1)
31 read_lock(&tasklist_lock); 27 return false;
32 do_each_thread(g, t) {
33 if (t->mm == mm && t != p)
34 goto no_unlock;
35 } while_each_thread(g, t);
36 read_unlock(&tasklist_lock);
37 }
38 28
39 return true; 29 if (atomic_read(&mm->mm_users) == 1)
30 return true;
31
32 ret = false;
33 down_write(&mm->mmap_sem);
34 rcu_read_lock();
35 for_each_process(p) {
36 if (unlikely(p->flags & PF_KTHREAD))
37 continue;
38 if (unlikely(p == task->group_leader))
39 continue;
40
41 t = p;
42 do {
43 if (unlikely(t->mm == mm))
44 goto found;
45 if (likely(t->mm))
46 break;
47 } while_each_thread(p, t);
48 }
49 ret = true;
50found:
51 rcu_read_unlock();
52 up_write(&mm->mmap_sem);
40 53
41no_unlock: 54 return ret;
42 read_unlock(&tasklist_lock);
43no:
44 return false;
45} 55}