linux-kernel - Re: [PATCH] virtio: suppress kmemleak false positive

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Date:	Fri, 11 Jan 2013 16:43:04 +0200
From:	Daniel Baluta <daniel.baluta@...il.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Alexandru Copot <alex.mihai.c@...il.com>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"mst@...hat.com" <mst@...hat.com>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] virtio: suppress kmemleak false positive

On Fri, Jan 11, 2013 at 4:32 PM, Daniel Baluta <daniel.baluta@...il.com> wrote:
>
>
> On Fri, Jan 11, 2013 at 4:02 PM, Catalin Marinas <catalin.marinas@....com>
> wrote:
>>
>> 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@...il.com>
>> > CC: Daniel Baluta <dbaluta@...acom.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.
>>
>
> 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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