Re: general protection fault in put_pid

Shakeel Butt
2019-01-07T18:22:41Z

On Mon, Jan 7, 2019 at 10:04 AM Manfred Spraul
<manfred@colorfullife.com> wrote:
>
> On 1/3/19 11:18 PM, Shakeel Butt wrote:
> > Hi Manfred,
> >
> > On Sun, Dec 23, 2018 at 4:26 AM Manfred Spraul
> > <manfred@colorfullife.com> wrote:
> >> Hello Dmitry,
> >>
> >> On 12/23/18 10:57 AM, Dmitry Vyukov wrote:
> >>> I can reproduce this infinite memory consumption with the C
> >>> program:
> >>> https://gist.githubusercontent.com/dvyukov/03ec54b3429ade16fa07bf8b2379aff3/raw/ae4f654e279810de2505e8fa41b73dc1d77778e6/gistfile1.txt
> >>>
> >>> But this is working as intended, right? It just creates infinite
> >>> number of large semaphore sets, which reasonably consumes infinite
> >>> amount of memory.
> >>> Except that it also violates the memcg bound and a process can
> >>> have
> >>> effectively unlimited amount of such "drum memory" in semaphores.
> >> Yes, this is as intended:
> >>
> >> If you call semget(), then you can use memory, up to the limits in
> >> /proc/sys/kernel/sem.
> >>
> >> Memcg is not taken into account, an admin must set
> >> /proc/sys/kernel/sem.
> >>
> >> The default are "infinite amount of memory allowed", as this is the
> >> most
> >> sane default: We had a logic that tried to autotune (i.e.: a new
> >> namespace "inherits" a fraction of the parent namespaces memory
> >> limits),
> >> but this we more or less always wrong.
> >>
> >>
> > What's the disadvantage of setting the limits in
> > /proc/sys/kernel/sem
> > high and let the task's memcg limits the number of semaphore a
> > process
> > can create? Please note that the memory underlying shmget and msgget
> > is already accounted to memcg.
>
> Nothing, it it just a question of implementing it.
>

I think it should be something like following:

---
ipc/sem.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 745dc6187e84..ad63df2658aa 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -494,7 +494,7 @@ static struct sem_array *sem_alloc(size_t nsems)
return NULL;

size = sizeof(*sma) + nsems * sizeof(sma->sems[0]);
- sma = kvmalloc(size, GFP_KERNEL);
+ sma = kvmalloc(size, GFP_KERNEL_ACCOUNT);
if (unlikely(!sma))
return NULL;

@@ -1897,7 +1897,8 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
rcu_read_unlock();

/* step 2: allocate new undo structure */
- new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
+ new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems,
+ GFP_KERNEL_ACCOUNT);
if (!new) {
ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
return ERR_PTR(-ENOMEM);
--
2.20.1.97.g81188d93c3-goog