Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

Cyrill Gorcunov
2012-02-16T19:29:58Z

On Thu, Feb 16, 2012 at 08:03:21PM +0100, Oleg Nesterov wrote:
> On 02/16, Cyrill Gorcunov wrote:
> >
> > On Thu, Feb 16, 2012 at 06:40:47PM +0100, Oleg Nesterov wrote:
> > > On 02/16, Cyrill Gorcunov wrote:
> > > >
> > > > -static void access_unlock(struct task_struct *task)
> > > > +static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
> > > > {
> > > > - mutex_unlock(&task->signal->cred_guard_mutex);
> > > > + if (m2 > m1)
> > > > + swap(m1, m2);
> > >
> > > Well, the order doesn't matter in case of _unlock, you can remove
> > > this part. Not that it really hurts though, I won't argue.
> >
> > It drops some instructions so I think it worth removing
>
> Yes.
>

Final one ;) I agreed on every line of your comment, thanks a lot Oleg!
---
From: Cyrill Gorcunov <gorcunov@openvz.org>
Subject: syscalls, x86: Make __NR_kcmp to work with equivalent pids

In case if pid1 is equal to pid2 the kcmp will return -EBUSY,
which makes no sence. Make it able to work with equivalent pids.
Selftest is extended as well.

Repored-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---
diff -u linux-2.6.git/kernel/kcmp.c linux-2.6.git/kernel/kcmp.c
--- linux-2.6.git/kernel/kcmp.c
+++ linux-2.6.git/kernel/kcmp.c
@@ -58,22 +58,28 @@
return file;
}

-static void access_unlock(struct task_struct *task)
+static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
{
- mutex_unlock(&task->signal->cred_guard_mutex);
+ if (likely(m2 != m1))
+ mutex_unlock(m2);
+ mutex_unlock(m1);
}

-static int access_trylock(struct task_struct *task)
+static int kcmp_lock(struct mutex *m1, struct mutex *m2)
{
- if (!mutex_trylock(&task->signal->cred_guard_mutex))
- return -EBUSY;
+ int err;

- if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
- mutex_unlock(&task->signal->cred_guard_mutex);
- return -EPERM;
+ if (m2 > m1)
+ swap(m1, m2);
+
+ err = mutex_lock_killable(m1);
+ if (!err && likely(m1 != m2)) {
+ err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING);
+ if (err)
+ mutex_unlock(m1);
}

- return 0;
+ return err;
}

SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
@@ -100,12 +106,15 @@
/*
* One should have enough rights to inspect task details.
*/
- ret = access_trylock(task1);
+ ret = kcmp_lock(&task1->signal->cred_guard_mutex,
+ &task2->signal->cred_guard_mutex);
if (ret)
goto err;
- ret = access_trylock(task2);
- if (ret)
+ if (!ptrace_may_access(task1, PTRACE_MODE_READ) ||
+ !ptrace_may_access(task2, PTRACE_MODE_READ)) {
+ ret = -EPERM;
goto err_unlock;
+ }

switch (type) {
case KCMP_FILE: {
@@ -149,9 +158,9 @@
break;
}

- access_unlock(task2);
err_unlock:
- access_unlock(task1);
+ kcmp_unlock(&task1->signal->cred_guard_mutex,
+ &task2->signal->cred_guard_mutex);
err:
put_task_struct(task1);
put_task_struct(task2);
diff -u linux-2.6.git/tools/testing/selftests/kcmp/kcmp_test.c linux-2.6.git/tools/testing/selftests/kcmp/kcmp_test.c
--- linux-2.6.git/tools/testing/selftests/kcmp/kcmp_test.c
+++ linux-2.6.git/tools/testing/selftests/kcmp/kcmp_test.c
@@ -74,6 +74,15 @@
ret = -1;
} else
printf("PASS: 0 returned as expected\n");
+
+ /* Compare with self */
+ ret = sys_kcmp(pid1, pid1, KCMP_VM, 0, 0);
+ if (ret) {
+ printf("FAIL: 0 expected but %li returned\n", ret);
+ ret = -1;
+ } else
+ printf("PASS: 0 returned as expected\n");
+
exit(ret);
}