On 04/24/2017 04:35 PM, Dr. David Alan Gilbert wrote: > * Christian Borntraeger (borntrae...@de.ibm.com) wrote: >> On 04/24/2017 12:53 PM, Dr. David Alan Gilbert wrote: >>> * Christian Borntraeger (borntrae...@de.ibm.com) wrote: >>>> David, Juan, >>>> >>>> I can trigger a hang of postcopy migration (when I do it early) so >>>> that both sides are in paused state. Looks like one thread is still >>>> loading vmstates for virtio and this load accesses guest memory and >>>> triggers a userfault. >>> >>> It's perfectly legal for the destination to cause a userfault as it >>> loads the virtio queue - the virtio queue should be being loaded by >>> the main thread from the buffer while the 'listening' thread is >>> waiting for the incoming page data. >>> >>> Can you turn on the following tracing please: destination: >>> postcopy_ram_fault_thread_request postcopy_place_page >>> postcopy_place_page_zero >>> >>> source: migrate_handle_rp_req_pages ram_save_queue_pages >>> >>> You should see: virtio does the access userfault generates a fault >>> postcopy_ram_fault_thread_request sends the request to the source >>> >>> the source sees migrate_handle_rp_req_pages queues it with >>> ram_save_queue_pages >>> >>> the destination sees the page arrive and postcopy_place_page or >>> postcopy_place_page_zero >>> >>> some of that might disappear if the page was already on it's way. >> >> >> the last event on the source are >> [..] >> 58412@1493037953.747988:postcopy_place_page host=0x3ff92246000 >> 58412@1493037953.747992:postcopy_place_page host=0x3ff92247000 > > How do you see those on the source???
It was the previous migrate (I did it in a loop forth and back) The problem happens on the migrate back. > >> 58412@1493037956.804210:migrate_handle_rp_req_pages in s390.ram at 41d9000 >> len 1000 >> 58412@1493037956.804216:ram_save_queue_pages s390.ram: start: 41d9000 len: >> 100 >> > > Is that a typo? I'm expecting those two 'len' fields to be the same? Yes, its a cut'n' paste "miss the last byte" > >> On the target a see lots of >> >> 39741@1493037958.833710:postcopy_place_page_zero host=0x3ff9befa000 >> 39741@1493037958.833716:postcopy_place_page host=0x3ff9befb000 >> 39741@1493037958.833759:postcopy_place_page host=0x3ff9befc000 >> 39741@1493037958.833818:postcopy_place_page host=0x3ff9befd000 >> 39741@1493037958.833819:postcopy_place_page_zero host=0x3ff9befe000 >> 39741@1493037958.833822:postcopy_place_page host=0x3ff9beff000 >> >> So we have about 2 seconds of traffic going on after that request, >> I assume its precopy related. >> >> Looking back on the target history there was >> 39741@1493037956.804337:postcopy_ram_fault_thread_request Request for >> HVA=3ff618d9000 rb=s390.ram offset=41d9000 >> >> In fact it seems to be the first and only request: >> >> # cat /tmp/test0.trace | grep -v postcopy_place_page >> >> 39741@1493037956.804337:postcopy_ram_fault_thread_request Request for >> HVA=3ff618d9000 rb=s390.ram offset=41d9000 > > OK, does the HVA there correspond to the address that your virtio device is > blocking on? yes it is the same page. > (or at least the start of the page) > Do you see a postcopy_place_page with a host= the same HVA ? no > > From the source backtrace, I think the source thinks it's sent everything > and is waiting for the return-path-thread to close. > > Dave > >>> >>> Dave >>> >>>> Thread 1 (Thread 0x3ffa2f45f00 (LWP 21122)): #0 0x0000000001017130 >>>> in lduw_he_p (ptr=0x3ff498d9002) at >>>> /root/qemu/include/qemu/bswap.h:317 <---- according to the host >>>> kernel this threads hangs in handle_userfault. #1 >>>> 0x0000000001017342 in lduw_le_p (ptr=0x3ff498d9002) at >>>> /root/qemu/include/qemu/bswap.h:359 #2 0x0000000001025840 in >>>> address_space_lduw_internal_cached (cache=0x283491d0, addr=2, >>>> attrs=..., result=0x0, endian=DEVICE_LITTLE_ENDIAN) at >>>> /root/qemu/memory_ldst.inc.c:284 #3 0x00000000010259a6 in >>>> address_space_lduw_le_cached (cache=0x283491d0, addr=2, attrs=..., >>>> result=0x0) at /root/qemu/memory_ldst.inc.c:315 #4 >>>> 0x0000000001025ad6 in lduw_le_phys_cached (cache=0x283491d0, >>>> addr=2) at /root/qemu/memory_ldst.inc.c:334 #5 0x0000000001116c10 >>>> in virtio_lduw_phys_cached (vdev=0x28275090, cache=0x283491d0, >>>> pa=2) at /root/qemu/include/hw/virtio/virtio-access.h:166 #6 >>>> 0x0000000001117940 in vring_used_idx (vq=0x3ffa2e1c090) at >>>> /root/qemu/hw/virtio/virtio.c:263 #7 0x000000000111daea in >>>> virtio_load (vdev=0x28275090, f=0x28353600, version_id=2) at >>>> /root/qemu/hw/virtio/virtio.c:2168 #8 0x000000000111d0cc in >>>> virtio_device_get (f=0x28353600, opaque=0x28275090, size=0, >>>> field=0x16adf38 <__compound_literal.0>) at >>>> /root/qemu/hw/virtio/virtio.c:1975 #9 0x00000000012a7f50 in >>>> vmstate_load_state (f=0x28353600, vmsd=0x14db480 >>>> <vmstate_virtio_blk>, opaque=0x28275090, version_id=2) at >>>> /root/qemu/migration/vmstate.c:128 #10 0x00000000010cbc08 in >>>> vmstate_load (f=0x28353600, se=0x28279e60, version_id=2) at >>>> /root/qemu/migration/savevm.c:732 #11 0x00000000010ced6e in >>>> qemu_loadvm_section_start_full (f=0x28353600, mis=0x17169a8 >>>> <mis_current>) at /root/qemu/migration/savevm.c:1890 #12 >>>> 0x00000000010cf00c in qemu_loadvm_state_main (f=0x28353600, >>>> mis=0x17169a8 <mis_current>) at /root/qemu/migration/savevm.c:1947 >>>> #13 0x00000000010ce5bc in loadvm_handle_cmd_packaged (mis=0x17169a8 >>>> <mis_current>) at /root/qemu/migration/savevm.c:1707 #14 >>>> 0x00000000010ce87e in loadvm_process_command (f=0x282c7d20) at >>>> /root/qemu/migration/savevm.c:1770 #15 0x00000000010cf056 in >>>> qemu_loadvm_state_main (f=0x282c7d20, mis=0x17169a8 <mis_current>) >>>> at /root/qemu/migration/savevm.c:1960 #16 0x00000000010cf2b6 in >>>> qemu_loadvm_state (f=0x282c7d20) at >>>> /root/qemu/migration/savevm.c:2020 #17 0x000000000129d234 in >>>> process_incoming_migration_co (opaque=0x282c7d20) at >>>> /root/qemu/migration/migration.c:404 #18 0x00000000014b6ca2 in >>>> coroutine_trampoline (i0=0, i1=674533168) at >>>> /root/qemu/util/coroutine-ucontext.c:79 #19 0x000003ff8de530ea in >>>> __makecontext_ret () from target:/lib64/libc.so.6 >>>> >>>> Thread 8 (Thread 0x3ff40b38910 (LWP 21165)): #0 0x000003ff8df04336 >>>> in syscall () from target:/lib64/libc.so.6 #1 0x00000000014933ce >>>> in qemu_futex_wait (f=0x17169b0 <mis_current+8>, val=4294967295) at >>>> /root/qemu/include/qemu/futex.h:26 #2 0x00000000014935d0 in >>>> qemu_event_wait (ev=0x17169b0 <mis_current+8>) at >>>> /root/qemu/util/qemu-thread-posix.c:399 #3 0x00000000010ce094 in >>>> postcopy_ram_listen_thread (opaque=0x282c7d20) at >>>> /root/qemu/migration/savevm.c:1532 #4 0x000003ff8e007bc4 in >>>> start_thread () from target:/lib64/libpthread.so.0 #5 >>>> 0x000003ff8df0a9f2 in thread_start () from target:/lib64/libc.so.6 >>>> >>>> Thread 7 (Thread 0x3ff41338910 (LWP 21164)): #0 0x000003ff8defd72c >>>> in ?? () from target:/lib64/libc.so.6 #1 0x00000000012af920 in >>>> postcopy_ram_fault_thread (opaque=0x17169a8 <mis_current>) at >>>> /root/qemu/migration/postcopy-ram.c:437 #2 0x000003ff8e007bc4 in >>>> start_thread () from target:/lib64/libpthread.so.0 #3 >>>> 0x000003ff8df0a9f2 in thread_start () from target:/lib64/libc.so.6 >>>> >>>> Thread 6 (Thread 0x3ff41b38910 (LWP 21163)): #0 0x000003ff8e00d450 >>>> in pthread_cond_wait@@GLIBC_2.3.2 () from >>>> target:/lib64/libpthread.so.0 #1 0x0000000001492d66 in >>>> qemu_cond_wait (cond=0x28302408, mutex=0x283023e0) at >>>> /root/qemu/util/qemu-thread-posix.c:133 #2 0x00000000010c6080 in >>>> do_data_decompress (opaque=0x283023d8) at >>>> /root/qemu/migration/ram.c:2277 #3 0x000003ff8e007bc4 in >>>> start_thread () from target:/lib64/libpthread.so.0 #4 >>>> 0x000003ff8df0a9f2 in thread_start () from target:/lib64/libc.so.6 >>>> >>>> Thread 5 (Thread 0x3ff42338910 (LWP 21162)): #0 0x000003ff8e00d450 >>>> in pthread_cond_wait@@GLIBC_2.3.2 () from >>>> target:/lib64/libpthread.so.0 #1 0x0000000001492d66 in >>>> qemu_cond_wait (cond=0x28302390, mutex=0x28302368) at >>>> /root/qemu/util/qemu-thread-posix.c:133 #2 0x00000000010c6080 in >>>> do_data_decompress (opaque=0x28302360) at >>>> /root/qemu/migration/ram.c:2277 #3 0x000003ff8e007bc4 in >>>> start_thread () from target:/lib64/libpthread.so.0 #4 >>>> 0x000003ff8df0a9f2 in thread_start () from target:/lib64/libc.so.6 >>>> >>>> Thread 4 (Thread 0x3ff89287910 (LWP 21148)): #0 0x000003ff8e010abc >>>> in __lll_lock_wait () from target:/lib64/libpthread.so.0 #1 >>>> 0x000003ff8e00bcb6 in __pthread_mutex_cond_lock () from >>>> target:/lib64/libpthread.so.0 #2 0x000003ff8e00d4ee in >>>> pthread_cond_wait@@GLIBC_2.3.2 () from >>>> target:/lib64/libpthread.so.0 #3 0x0000000001492d66 in >>>> qemu_cond_wait (cond=0x2831eb00, mutex=0x1711688 >>>> <qemu_global_mutex>) at /root/qemu/util/qemu-thread-posix.c:133 #4 >>>> 0x000000000107720e in qemu_kvm_wait_io_event (cpu=0x282e09b0) at >>>> /root/qemu/cpus.c:1085 #5 0x00000000010773aa in >>>> qemu_kvm_cpu_thread_fn (arg=0x282e09b0) at /root/qemu/cpus.c:1123 >>>> #6 0x000003ff8e007bc4 in start_thread () from >>>> target:/lib64/libpthread.so.0 #7 0x000003ff8df0a9f2 in >>>> thread_start () from target:/lib64/libc.so.6 >>>> >>>> Thread 3 (Thread 0x3ff8a7ff910 (LWP 21145)): #0 0x000003ff8defd832 >>>> in ppoll () from target:/lib64/libc.so.6 #1 0x000000000148b092 in >>>> qemu_poll_ns (fds=0x3ff840008c0, nfds=1, timeout=-1) at >>>> /root/qemu/util/qemu-timer.c:322 #2 0x000000000148f46a in aio_poll >>>> (ctx=0x2827e7b0, blocking=true) at /root/qemu/util/aio-posix.c:622 >>>> #3 0x00000000011a78f6 in iothread_run (opaque=0x2827d740) at >>>> /root/qemu/iothread.c:59 #4 0x000003ff8e007bc4 in start_thread () >>>> from target:/lib64/libpthread.so.0 #5 0x000003ff8df0a9f2 in >>>> thread_start () from target:/lib64/libc.so.6 >>>> >>>> Thread 2 (Thread 0x3ff8afff910 (LWP 21142)): #0 0x000003ff8df04336 >>>> in syscall () from target:/lib64/libc.so.6 #1 0x00000000014933ce >>>> in qemu_futex_wait (f=0x1b2b9b4 <rcu_call_ready_event>, >>>> val=4294967295) at /root/qemu/include/qemu/futex.h:26 #2 >>>> 0x00000000014935d0 in qemu_event_wait (ev=0x1b2b9b4 >>>> <rcu_call_ready_event>) at /root/qemu/util/qemu-thread-posix.c:399 >>>> #3 0x00000000014b3e40 in call_rcu_thread (opaque=0x0) at >>>> /root/qemu/util/rcu.c:249 #4 0x000003ff8e007bc4 in start_thread () >>>> from target:/lib64/libpthread.so.0 #5 0x000003ff8df0a9f2 in >>>> thread_start () from target:/lib64/libc.so.6 >>>> >>>> >>>> Looks like that this <qemu:arg value='-drive'/> <qemu:arg >>>> value='driver=null-aio,id=null1,if=none,size=100G'/> <qemu:arg >>>> value='-device'/> <qemu:arg >>>> value='virtio-blk-ccw,scsi=off,drive=null1,serial=null1,num-queues=4'/> >>>> >>>> >>>> is necessary to trigger the hang, with nun-qeues=1 everything seems to >>>> work fine, so it might >>>> be a virtio issue after all? >>>>