On Mon, 2017-10-02 at 17:21 +0200, Oleg Nesterov wrote:

Hi Rik,

On 10/02, Rik van Riel wrote:

Gargi and I are looking at that code, and trying to figure out
exactly what needs to be done to make all of this correct.

see another email I sent to Gargi a minute ago,

2) With pid_ns_prepare_proc out of the way, we can put all the code    from below where the call to pid_ns_prepare_proc is now (except    error handing) into the main loop of pid allocation, so we can    do all that stuff under the pidmap_lock:

   for (i = ns->level; i >= 0; i--) {
       ...
       idr_alloc_cyclic(...)
       get_pid_ns(ns);
       atomic_set(&pid->count, 1);
       for (...)
            INIT_HLIST_HEAD(...)        ns->nr_allocated++;
       ...
  }

I do not see how this can fix the problem with not-fully-initialized
pid returned by find_pid_ns().

As for PIDNS_ADDING/PIDNS_HASH_ADDING, _perhaps_ we can cleanup this
logic
a bit and do the check earlier, but imo this needs another/separate
change.

I'd suggest to keep the current logic and the order of initialization
and
just do

for (i = ns->level; i >= 0; i--) {
...

// do not expose the new pid to find_pid_ns() until it
// is fully initialized
nr = idr_alloc_cyclic(&tmp->idr, /*pid*/ NULL, ...);
...
}

...

spin_lock_irq(&pidmap_lock);
if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
goto out_unlock;
for ( ; upid >= pid->numbers; --upid) {
- hlist_add_head_rcu(&upid->pid_chain,
- &pid_hash[pid_hashfn(upid->nr, upid-

ns)]);

+ // finally make it visible to find_pid_ns()
+ idr_replace(upid->ns-idr, pid, upid->nr);
upid->ns->nr_hashed++;
}
spin_unlock_irq(&pidmap_lock);

Or I missed something?

You are right, that would both fix the problem, and keep the error
paths relatively simple.

Gargi, what do you think?

--
All Rights Reversed.
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--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Mon, Oct 2, 2017 at 8:52 PM, Rik van Riel <[email protected]> wrote:

On Mon, 2017-10-02 at 17:21 +0200, Oleg Nesterov wrote:

Hi Rik,

On 10/02, Rik van Riel wrote:

Gargi and I are looking at that code, and trying to figure out
exactly what needs to be done to make all of this correct.

see another email I sent to Gargi a minute ago,

2) With pid_ns_prepare_proc out of the way, we can put all the code
from below where the call to pid_ns_prepare_proc is now (except
error handing) into the main loop of pid allocation, so we can
do all that stuff under the pidmap_lock:

for (i = ns->level; i >= 0; i--) {
...
idr_alloc_cyclic(...)
get_pid_ns(ns);
atomic_set(&pid->count, 1);
for (...)
INIT_HLIST_HEAD(...)
ns->nr_allocated++;
...
}

I do not see how this can fix the problem with not-fully-initialized
pid returned by find_pid_ns().

As for PIDNS_ADDING/PIDNS_HASH_ADDING, _perhaps_ we can cleanup this
logic
a bit and do the check earlier, but imo this needs another/separate
change.

I'd suggest to keep the current logic and the order of initialization
and
just do

for (i = ns->level; i >= 0; i--) {
...

// do not expose the new pid to find_pid_ns() until it
// is fully initialized
nr = idr_alloc_cyclic(&tmp->idr, /*pid*/ NULL, ...);
...
}

...

spin_lock_irq(&pidmap_lock);
if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
goto out_unlock;
for ( ; upid >= pid->numbers; --upid) {
- hlist_add_head_rcu(&upid->pid_chain,
- &pid_hash[pid_hashfn(upid->nr, upid-

ns)]);

+ // finally make it visible to find_pid_ns()
+ idr_replace(upid->ns-idr, pid, upid->nr);
upid->ns->nr_hashed++;
}
spin_unlock_irq(&pidmap_lock);

Or I missed something?

Thanks for detailed explanation Oleg!

You are right, that would both fix the problem, and keep the error
paths relatively simple.

Gargi, what do you think?

I understand better now. Thanks!

Best,
Gargi

--
All Rights Reversed.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)