Re: [PATCH] virtio: suppress kmemleak false positive

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, Jan 11, 2013 at 01:51:43PM +0000, Alexandru Copot wrote:
> While doing simple IPv6 tests in KVM virtual machines,
> (add an IPv6 address to eth0) kmemleak complains about
> an unreferenced object:
> 
> unreferenced object 0xffff88001e804120 (size 32):
>   comm "softirq", pid 0, jiffies 4294900928 (age 631.544s)
>   hex dump (first 32 bytes):
>     28 cb fd 1d 00 00 00 00 0c 00 00 00 01 00 01 00  (...............
>     02 d0 83 1d 00 00 00 00 6e 00 00 00 00 00 00 00  ........n.......
>   backtrace:
>     [<ffffffff815ed721>] kmemleak_alloc+0x21/0x50
>     [<ffffffff8111d0b0>] __kmalloc+0xe0/0x160
>     [<ffffffff81362b7c>] virtqueue_add_buf+0x1fc/0x3d0
>     [<ffffffff8140cbd3>] start_xmit+0x153/0x3a0
>     [<ffffffff8150887e>] dev_hard_start_xmit+0x21e/0x470
>     [<ffffffff815247ce>] sch_direct_xmit+0xfe/0x280
>     [<ffffffff81509014>] dev_queue_xmit+0x1f4/0x5d0
>     [<ffffffff81592e91>] ip6_finish_output2+0x101/0x450
>     [<ffffffff81595ae8>] ip6_finish_output+0x98/0x200
>     [<ffffffff81595ca1>] ip6_output+0x51/0x1b0
>     [<ffffffff815b51af>] mld_sendpack+0x19f/0x360
>     [<ffffffff815b59b4>] mld_ifc_timer_expire+0x194/0x290
>     [<ffffffff8104b794>] call_timer_fn+0x74/0xf0
>     [<ffffffff8104bb1b>] run_timer_softirq+0x18b/0x220
>     [<ffffffff81045f81>] __do_softirq+0xe1/0x1c0
>     [<ffffffff8160a4fc>] call_softirq+0x1c/0x30
> 
> Seems the function vring_add_indirect stores an array of
> struct vring_desc by using virt_to_phys and kmemleak
> doesn't track the pointer.
> 
> The following patch can fix this.
> 
> Signed-off-by: Alexandru Copot <alex.mihai.c@gmail.com>
> CC: Daniel Baluta <dbaluta@ixiacom.com>
> ---
>  drivers/virtio/virtio_ring.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index ffd7e7d..e0b591b 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -23,6 +23,7 @@
>  #include <linux/slab.h>
>  #include <linux/module.h>
>  #include <linux/hrtimer.h>
> +#include <linux/kmemleak.h>
>  
>  /* virtio guest is communicating with a virtual "device" that actually runs on
>   * a host processor.  Memory barriers are used to control SMP effects. */
> @@ -140,6 +141,7 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
>  	desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
>  	if (!desc)
>  		return -ENOMEM;
> +	kmemleak_not_leak(desc);

Please add a comment above this call in case people later wonder why
this annotation is needed.

-- 
Catalin