Re: [Qemu-devel] Re: [PATCH v3 2/6] Introduce bit-based phys_ram_dirty for VGA, CODE, MIGRATION and MASTER.

[Yoshiaki Tamura]

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.