On 12/21/2012 11:39 AM, Eric Dumazet wrote:

On Fri, 2012-12-21 at 11:32 +0800, Jason Wang wrote:

quoted

On 12/21/2012 07:50 AM, Stephen Hemminger wrote:

quoted

On Thu, 20 Dec 2012 15:38:17 -0800
Eric Dumazet [off-list ref] wrote:

quoted

On Thu, 2012-12-20 at 18:16 -0500, Paul Moore wrote:

quoted

[CC'ing netdev in case this is a known problem I just missed ...]

Hi Jason,

I started doing some more testing with the multiqueue TUN changes and I ran 
into a problem when running tunctl: running it once w/o arguments works as 
expected, but running it a second time results in failure and a 
kmem_cache_sanity_check() failure.  The problem appears to be very repeatable 
on my test VM and happens independent of the LSM/SELinux fixup patches.

Have you seen this before?

Obviously code in tun_flow_init() is wrong...

static int tun_flow_init(struct tun_struct *tun)
{
        int i;

        tun->flow_cache = kmem_cache_create("tun_flow_cache",
                                            sizeof(struct tun_flow_entry), 0, 0,
                                            NULL);
        if (!tun->flow_cache)
                return -ENOMEM;
...
}


I have no idea why we would need a kmem_cache per tun_struct,
and why we even need a kmem_cache.

Normally flow malloc/free should be good enough.
It might make sense to use private kmem_cache if doing hlist_nulls.


Acked-by: Stephen Hemminger <redacted>

Should be at least a global cache, I thought I can get some speed-up by
using kmem_cache.

Acked-by: Jason Wang <jasowang@redhat.com>

Was it with SLUB or SLAB ?

Using generic kmalloc-64 is better than a dedicated kmem_cache of 48
bytes per object, as we guarantee each object is on a single cache line.

Right, thanks for the explanation.