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Date: Mon, 19 Apr 2010 20:52:26 +0900
From: Yoshiaki Tamura <tamura.yoshiaki@lab.ntt.co.jp>
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Subject: Re: [Qemu-devel] Re: [PATCH v3 2/6] Introduce bit-based phys_ram_dirty
	for VGA, CODE, MIGRATION and MASTER.
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To: Avi Kivity <avi@redhat.com>
Cc: aliguori@us.ibm.com, mtosatti@redhat.com, qemu-devel@nongnu.org, ohmura.kei@lab.ntt.co.jp

Avi Kivity wrote:
> On 04/19/2010 02:31 PM, Yoshiaki Tamura wrote:
>>
>>>>> typedef struct RAMBlock {
>>>>> @@ -2825,10 +2825,16 @@ ram_addr_t qemu_ram_alloc(ram_addr_t size)
>>>>> new_block->next = ram_blocks;
>>>>> ram_blocks = new_block;
>>>>>
>>>>> - phys_ram_dirty = qemu_realloc(phys_ram_dirty,
>>>>> - (last_ram_offset + size)>> TARGET_PAGE_BITS);
>>>>> - memset(phys_ram_dirty + (last_ram_offset>> TARGET_PAGE_BITS),
>>>>> - 0xff, size>> TARGET_PAGE_BITS);
>>>>> + if (BITMAP_SIZE(last_ram_offset + size) !=
>>>>> BITMAP_SIZE(last_ram_offset)) {
>>>> This check is unneeded - the code will work fine even if the bitmap
>>>> size
>>>> doesn't change.
>>> OK. I'll remove it.
>> I have a problem here.
>> If I remove this check, glibc reports an error as below.
>>
>> *** glibc detected *** /usr/local/qemu/bin/qemu-system-x86_64:
>> realloc(): invalid pointer: 0x0000000001f0e450 ***
>> ======= Backtrace: =========
>> /lib64/libc.so.6[0x369fa75a96]
>> /lib64/libc.so.6(realloc+0x2a1)[0x369fa7b881]
>> /usr/local/qemu/bin/qemu-system-x86_64[0x437d93]
>> /usr/local/qemu/bin/qemu-system-x86_64[0x4f03f6]
>> /usr/local/qemu/bin/qemu-system-x86_64[0x5b052c]
>> /usr/local/qemu/bin/qemu-system-x86_64[0x5b0d8b]
>> /usr/local/qemu/bin/qemu-system-x86_64[0x41ec2b]
>> /lib64/libc.so.6(__libc_start_main+0xfd)[0x369fa1ea2d]
>> /usr/local/qemu/bin/qemu-system-x86_64[0x406479]
>> ======= Memory map: ========
>>
>> I reminded that I put this check to avoid reallocating same size to
>> the bitmap.
>> qemu goes this routine at start up, and extends last_ram_offset at
>> small numbers.
>> The error above is reported at the extension phase.
>>
>
> This probably means that an old bitmap pointer leaked somewhere, and we
> realloc() it after free? Or perhaps a glibc bug.

Original qemu doesn't have a code the frees phys_ram_dirty, and I didn't either.
Hmmm.