Re: Recent change pmem related breaks Xen migration

[Beata Michalska <beata.michalska@linaro.org>]

Hi Anthony,

On Thu, 19 Dec 2019 at 15:42, Anthony PERARD <anthony.perard@citrix.com> wrote:
>
> Hi,
>
> Commit bd108a44bc29 ("migration: ram: Switch to ram block writeback")
> breaks migration on Xen. We have:
>   ramblock_ptr: Assertion `offset_in_ramblock(block, offset)' failed.
>
> I've track it down to qemu_ram_writeback() calling ramblock_ptr()
> unconditionally, even when the result will not be used.
>
> Maybe we could call ramblock_ptr() twice in that function? I've prepared
> a patch.
>
>
> FYI, full-ish trace on restore of a xen guest:
> #3  0x00007f82d0848526 in __assert_fail () from /usr/lib/libc.so.6
> #4  0x0000562dc4578122 in ramblock_ptr (block=0x562dc5ebe2a0, offset=0) at /root/build/qemu/include/exec/ram_addr.h:120
> #5  0x0000562dc457d1b7 in qemu_ram_writeback (block=0x562dc5ebe2a0, start=0, length=515899392) at /root/build/qemu/exec.c:2169
> #6  0x0000562dc45e8941 in qemu_ram_block_writeback (block=0x562dc5ebe2a0) at /root/build/qemu/include/exec/ram_addr.h:182
> #7  0x0000562dc45f0b56 in ram_load_cleanup (opaque=0x562dc510fe00 <ram_state>) at /root/build/qemu/migration/ram.c:3983
> #8  0x0000562dc49970b6 in qemu_loadvm_state_cleanup () at migration/savevm.c:2415
> #9  0x0000562dc4997548 in qemu_loadvm_state (f=0x562dc6a1c600) at migration/savevm.c:2597
> #10 0x0000562dc4987be7 in process_incoming_migration_co (opaque=0x0) at migration/migration.c:454
> #11 0x0000562dc4b907e5 in coroutine_trampoline (i0=-962514432, i1=22061) at util/coroutine-ucontext.c:115
>
> And *block in ramblock_ptr():
> (gdb) p *block
> $2 = {
>   rcu = {
>     next = 0x0,
>     func = 0x0
>   },
>   mr = 0x562dc512e140 <ram_memory>,
>   host = 0x0,
>   colo_cache = 0x0,
>   offset = 0,
>   used_length = 515899392,
>   max_length = 515899392,
>   resized = 0x0,
>   flags = 16,
>   idstr = "xen.ram", '\000' <repeats 248 times>,
>   next = {
>     le_next = 0x562dc67bf7e0,
>     le_prev = 0x562dc510f1a0 <ram_list+64>
>   },
>   ramblock_notifiers = {
>     lh_first = 0x0
>   },
>   fd = -1,
>   page_size = 4096,
>   bmap = 0x0,
>   receivedmap = 0x562dc6a24a60,
>   clear_bmap = 0x0,
>   clear_bmap_shift = 0 '\000'
> }
>
> Cheers,
>
> --
> Anthony PERARD

I have already replied to your patch submission.
Looks good and thanks for fixing .

BR
Beata