RE: [PATCH v3 3/3] vmstate: Fix memory leak in vmstate_handle_alloc()

[gaojinhao]

Hi, Dave,
I will check the code about vmstate_spapr_tce_table to figure out the problem 
of seg fault.
Thank you for your check.

Jinhao Gao

-----Original Message-----
From: Dr. David Alan Gilbert [mailto:dgilbert@redhat.com] 
Sent: 2021年2月8日 18:53
To: gaojinhao <gaojinhao@huawei.com>
Cc: qemu-ppc@nongnu.org; qemu-devel@nongnu.org; Michael S . Tsirkin 
<mst@redhat.com>; David Gibson <david@gibson.dropbear.id.au>; Greg Kurz 
<groug@kaod.org>; Marc-André Lureau <marcandre.lureau@redhat.com>; Stefan 
Berger <stefanb@linux.vnet.ibm.com>; Jason Wang <jasowang@redhat.com>; Juan 
Quintela <quintela@redhat.com>; Wanghaibin (D) <wanghaibin.wang@huawei.com>; 
zhukeqian <zhukeqian1@huawei.com>
Subject: Re: [PATCH v3 3/3] vmstate: Fix memory leak in vmstate_handle_alloc()

* Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
> * Jinhao Gao (gaojinhao@huawei.com) wrote:
> > Some memory allocated for fields having a flag of VMS_ALLOC in 
> > SaveState may not free before VM load vmsd in migration. So we 
> > pre-free memory before allocation in vmstate_handle_alloc() to avoid 
> > memleaks.
> > 
> > Reported-by: Euler Robot <euler.robot@huawei.com>
> > Signed-off-by: Jinhao Gao <gaojinhao@huawei.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> Yes, I think that's OK; it's actually pretty rare for this to happen; 
> normally inwards migrations either succeed or fail and exit; doing 
> multiple loads from snapshots is valid and I guess COLO hits this as well.
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

I'm having to unqueue this because it's triggering a seg fault on Power in 
iotest 267 (just run make check).

#2  0x0000000116d0d4c8 in vmstate_handle_alloc (opaque=<optimized out>, 
field=0x11799e0c8 <__compound_literal.1+312>, ptr=0x1001f8f14b0) at 
../qemu/migration/vmstate.c:73
#3  0x0000000116d0d4c8 in vmstate_load_state (f=0x1001f6d0000, vmsd=0x117928730 
<vmstate_spapr_tce_table>, opaque=0x1001f8f1400, version_id=<optimized out>) at 
../qemu/migration/vmstate.c:122
#4  0x0000000116fb4a4c in vmstate_load (f=0x1001f6d0000, se=0x1001fc7bc40) at 
../qemu/migration/savevm.c:910
#5  0x0000000116fb5010 in qemu_loadvm_section_start_full 
(f=f@entry=0x1001f6d0000, mis=<optimized out>) at 
../qemu/migration/savevm.c:2433

It's the mig_nb_table that Power is doing some special handling with; so it 
needs some more checking before we can fix this.

Dave

> > ---
> >  migration/vmstate.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/migration/vmstate.c b/migration/vmstate.c index 
> > e9d2aef66b..873f76739f 100644
> > --- a/migration/vmstate.c
> > +++ b/migration/vmstate.c
> > @@ -70,6 +70,7 @@ static void vmstate_handle_alloc(void *ptr, const 
> > VMStateField *field,
> >          gsize size = vmstate_size(opaque, field);
> >          size *= vmstate_n_elems(opaque, field);
> >          if (size) {
> > +            g_free(*(void **)ptr);
> >              *(void **)ptr = g_malloc(size);
> >          }
> >      }
> > --
> > 2.23.0
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK