On 27.04.2017 19:22, Oleg Nesterov wrote:
On 04/27, Kirill Tkhai wrote:
quoted
On 27.04.2017 19:12, Oleg Nesterov wrote:
quoted
On 04/26, Kirill Tkhai wrote:
quoted
On 26.04.2017 18:53, Oleg Nesterov wrote:
quoted
quoted
+static long set_last_pid_vec(struct pid_namespace *pid_ns,
+ struct pidns_ioc_req *req)
+{
+ char *str, *p;
+ int ret = 0;
+ pid_t pid;
+
+ read_lock(&tasklist_lock);
+ if (!pid_ns->child_reaper)
+ ret = -EINVAL;
+ read_unlock(&tasklist_lock);
+ if (ret)
+ return ret;
why do you need to check ->child_reaper under tasklist_lock? this looks pointless.
In fact I do not understand how it is possible to hit pid_ns->child_reaper == NULL,
there must be at least one task in this namespace, otherwise you can't open a file
which has f_op == ns_file_operations, no?
Sure, it's impossible to pick a pid_ns, if there is no the pid_ns's tasks. I added
it under impression of
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=dfda351c729733a401981e8738ce497eaffcaa00
but here it's completely wrong. It will be removed in v2.
Hmm. But if I read this commit correctly then we really need to check
pid_ns->child_reaper != NULL ?
Currently we can't pick an "empty" pid_ns. But after the commit above a task
can do sys_unshare(CLONE_NEWPID), another (or the same) task can open its
/proc/$pid/ns/pid_for_children and call ns_ioctl() before the 1st alloc_pid() ?
Another task can't open /proc/$pid/ns/pid_for_children before the 1st alloc_pid(),
because pid_for_children is available to open only after the 1st alloc_pid().
So, it's impossible to call ioctl() on it.
Ah, OK, I didn't notice the ns->child_reaper check in pidns_for_children_get().
But note that it doesn't need tasklist_lock too.
Hm, are there possible strange situations with memory ordering, when we see
ns->child_reaper of already died ns, which was placed in the same memory?
Do we have to use some memory barriers here?