On Fri, Jan 11, 2013 at 4:32 PM, Daniel Baluta [off-list ref] wrote:

On Fri, Jan 11, 2013 at 4:02 PM, Catalin Marinas [off-list ref]
wrote:

quoted

On Fri, Jan 11, 2013 at 01:51:43PM +0000, Alexandru Copot wrote:

quoted

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 <redacted>
CC: Daniel Baluta <redacted>
---
 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.

Thanks Cătălin.

So, kememleak cannot handle this kind of pointer aliases?
Also, I wonder if phys_to_virt(virt_to_phys(x)) == x holds true all the
time.

Sending this again as it seems that linux-kernel rejected it because
of HTML format.

Sorry for the noise.

thanks,
Daniel.
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