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authorOleg Nesterov <oleg@redhat.com>2009-07-17 09:09:36 +1000
committerJames Morris <jmorris@namei.org>2009-07-17 09:09:36 +1000
commitd2e3ee9b29f5de5b01e611b04e6fb29760589b01 (patch)
treead73b17c2c6b83050a948685a0a3af3f907de67f /lib/is_single_threaded.c
parent713c0ecdb888e9ef6f085e828555455c5916b07f (diff)
downloadlinux-stericsson-d2e3ee9b29f5de5b01e611b04e6fb29760589b01.tar.gz
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/is_single_threaded.c')
-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 @@
#include <linux/sched.h>
-/**
- * is_single_threaded - Determine if a thread group is single-threaded or not
- * @p: A task in the thread group in question
- *
- * This returns true if the thread group to which a task belongs is single
- * threaded, false if it is not.
+/*
+ * Returns true if the task does not share ->mm with another thread/process.
*/
-bool is_single_threaded(struct task_struct *p)
+bool is_single_threaded(struct task_struct *task)
{
- struct task_struct *g, *t;
- struct mm_struct *mm = p->mm;
-
- if (atomic_read(&p->signal->count) != 1)
- goto no;
-
- if (atomic_read(&p->mm->mm_users) != 1) {
- read_lock(&tasklist_lock);
- do_each_thread(g, t) {
- if (t->mm == mm && t != p)
- goto no_unlock;
- } while_each_thread(g, t);
- read_unlock(&tasklist_lock);
- }
+ struct mm_struct *mm = task->mm;
+ struct task_struct *p, *t;
+ bool ret;
+
+ might_sleep();
+
+ if (atomic_read(&task->signal->live) != 1)
+ return false;
- return true;
+ if (atomic_read(&mm->mm_users) == 1)
+ return true;
+
+ ret = false;
+ down_write(&mm->mmap_sem);
+ rcu_read_lock();
+ for_each_process(p) {
+ if (unlikely(p->flags & PF_KTHREAD))
+ continue;
+ if (unlikely(p == task->group_leader))
+ continue;
+
+ t = p;
+ do {
+ if (unlikely(t->mm == mm))
+ goto found;
+ if (likely(t->mm))
+ break;
+ } while_each_thread(p, t);
+ }
+ ret = true;
+found:
+ rcu_read_unlock();
+ up_write(&mm->mmap_sem);
-no_unlock:
- read_unlock(&tasklist_lock);
-no:
- return false;
+ return ret;
}