Re: [Qemu-devel] [PATCH] exec: Stop using memory after free

[Don Slutz <don.slutz@gmail.com>]

On 12/01/15 04:52, Paolo Bonzini wrote:
> 
> 
> On 30/11/2015 23:11, Don Slutz wrote:
>> memory_region_unref(mr) can free memory.
>>
>> For example I got:
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> [Switching to Thread 0x7f43280d4700 (LWP 4462)]
>> 0x00007f43323283c0 in phys_section_destroy (mr=0x7f43259468b0)
>>     at /home/don/xen/tools/qemu-xen-dir/exec.c:1023
>> 1023        if (mr->subpage) {
>> (gdb) bt
>>     at /home/don/xen/tools/qemu-xen-dir/exec.c:1023
>>     at /home/don/xen/tools/qemu-xen-dir/exec.c:1034
>>     at /home/don/xen/tools/qemu-xen-dir/exec.c:2205
>> (gdb) p mr
>> $1 = (MemoryRegion *) 0x7f43259468b0
>>
>> And this change prevents this.
> 
> Great, thanks!  I think this fixes also the problem that Gonglei was
> seeing a few months ago.  I'll queue it for 2.5.
> 

Thanks.

> BTW, since I have your attention, have you noticed my refresh/rewrite of
> your SAS1068 patches?  A review would be welcome.
> 

It has been on the list of things to do.  Since I no longer work for
Verizon, it is now a non-work time event.  I also not longer have access
to the testing machines that I had used.

   -Don Slutz

> Paolo
> 
>> Signed-off-by: Don Slutz <Don.Slutz@Gmail.com>
>> ---
>>  exec.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/exec.c b/exec.c
>> index de1cf19..0bf0a6e 100644
>> --- a/exec.c
>> +++ b/exec.c
>> @@ -1064,9 +1064,11 @@ static uint16_t phys_section_add(PhysPageMap *map,
>>  
>>  static void phys_section_destroy(MemoryRegion *mr)
>>  {
>> +    bool have_sub_page = mr->subpage;
>> +
>>      memory_region_unref(mr);
>>  
>> -    if (mr->subpage) {
>> +    if (have_sub_page) {
>>          subpage_t *subpage = container_of(mr, subpage_t, iomem);
>>          object_unref(OBJECT(&subpage->iomem));
>>          g_free(subpage);
>>