* Claudio Fontana (cfont...@suse.de) wrote: > Hello all, > > during unrelated work for splitting QTest from the TCG instruction counting > module, > > I encountered what seems to be a migration stream issue, which is apparent > only on s390, and only shows in block test 267. > > ./check -qcow2 267 > > when it comes to snapshot save and load using backing file. > > Here is a minimal reproducer patch that causes the issue on s390 only. > > --------------------------------------------cut------------------------------------------- > diff --git a/cpus.c b/cpus.c > index 41d1c5099f..443b88697a 100644 > --- a/cpus.c > +++ b/cpus.c > @@ -643,7 +643,7 @@ static void qemu_account_warp_timer(void) > > static bool icount_state_needed(void *opaque) > { > - return use_icount; > + return 0; > }
That's weird; I mean that's just turning a subsection on and off; so you'd hope if this is a test that generates it's own snapshot and then uses it then it should be consistent. > static bool warp_timer_state_needed(void *opaque) > --------------------------------------------cut------------------------------------------- > > config.status configure line: > exec '/home/cfontana/qemu-build/../qemu/configure' '--enable-tcg' > '--disable-kvm' '--disable-hax' '--target-list=s390x-softmmu' '--enable-debug' > > $ make check-block > > TEST iotest-qcow2: 267 [fail] > QEMU -- > "/home/cfontana/qemu-build/tests/qemu-iotests/../../s390x-softmmu/qemu-system-s390x" > -nodefaults -display none -accel qtest > QEMU_IMG -- > "/home/cfontana/qemu-build/tests/qemu-iotests/../../qemu-img" > QEMU_IO -- "/home/cfontana/qemu-build/tests/qemu-iotests/../../qemu-io" > --cache writeback --aio threads -f qcow2 > QEMU_NBD -- > "/home/cfontana/qemu-build/tests/qemu-iotests/../../qemu-nbd" > IMGFMT -- qcow2 (compat=1.1) > IMGPROTO -- file > PLATFORM -- Linux/s390x s390zp13 5.3.18-21-default > TEST_DIR -- /home/cfontana/qemu-build/tests/qemu-iotests/scratch > SOCK_DIR -- /tmp/tmp.bLJcJVtzk5 > SOCKET_SCM_HELPER -- > /home/cfontana/qemu-build/tests/qemu-iotests/socket_scm_helper > > --- /home/cfontana/qemu/tests/qemu-iotests/267.out 2020-07-12 > 05:10:07.948262675 -0400 > +++ /home/cfontana/qemu-build/tests/qemu-iotests/267.out.bad 2020-07-12 > 05:27:03.358362781 -0400 > @@ -137,6 +137,9 @@ > ID TAG VM SIZE DATE VM CLOCK > -- snap0 SIZE yyyy-mm-dd hh:mm:ss 00:00:00.000 > (qemu) loadvm snap0 > +Unexpected storage key flag data: 0 > +error while loading state for instance 0x0 of device 's390-skeys' > +Error: Error -22 while loading VM state > (qemu) quit > > > ----------- > > > Not run: 172 186 192 259 287 > Failures: 267 > Failed 1 of 115 iotests > make: *** [/home/cfontana/qemu/tests/Makefile.include:880: > check-tests/check-block.sh] Error 1 > > ----------- > > Note: only the === -blockdev with a backing file === part of test 267 fails. > -blockdev with NBD is ok, like all the rest. > > > Interesting facts about s390 in particular: its save/load code includes the > transfer of "storage keys", > which include a buffer of 32768 bytes of keydata in the stream. > > The code (hw/s390x/s390-skeys.c), > is modeled similarly to RAM transfer (like in migration/ram.c), with an EOS > (end of stream) marker. > > Countrary to RAM transfer code though, after qemu_put_be64(f, EOS), the s390 > code does not qemu_fflush(f). > > ---------- > Observation: the migration/qemu-file.c shows an IO_BUF_SIZE of 32768. > > -- > > The following workarounds hide the problem (make the test pass): > > 1) always including the icount field in the (unrelated) timers field that are > sent before in the migration stream (ie not applying the reproducer patch). > > 2) increasing the IO_BUF_SIZE also hides the problem: > > ----------------------cut-------------------------- > diff --git a/migration/qemu-file.c b/migration/qemu-file.c > index be21518c57..f81d1272eb 100644 > --- a/migration/qemu-file.c > +++ b/migration/qemu-file.c > @@ -30,7 +30,7 @@ > #include "trace.h" > #include "qapi/error.h" > > -#define IO_BUF_SIZE 32768 > +#define IO_BUF_SIZE 65536 > #define MAX_IOV_SIZE MIN_CONST(IOV_MAX, 64) > > struct QEMUFile { > ----------------------cut-------------------------- > > 3) adding a qemu_fflush in hw/s390x/s390-skeys.c after EOS also "fixes" the > problem: > > ----------------------cut-------------------------- > diff --git a/hw/s390x/s390-skeys.c b/hw/s390x/s390-skeys.c > index 1e036cc602..47c9a015af 100644 > --- a/hw/s390x/s390-skeys.c > +++ b/hw/s390x/s390-skeys.c > @@ -252,6 +252,8 @@ static const TypeInfo qemu_s390_skeys_info = { > .class_size = sizeof(S390SKeysClass), > }; > > +extern void qemu_fflush(QEMUFile *f); > + > static void s390_storage_keys_save(QEMUFile *f, void *opaque) > { > S390SKeysState *ss = S390_SKEYS(opaque); > @@ -302,6 +304,7 @@ static void s390_storage_keys_save(QEMUFile *f, void > *opaque) > g_free(buf); > end_stream: > qemu_put_be64(f, eos); > + qemu_fflush(f); > } > > static int s390_storage_keys_load(QEMUFile *f, void *opaque, int version_id) > ----------------------cut-------------------------- > > Do any of you with better understanding of migration/, block and s390 have a > suggestion on what could be the issue here, > and what could be the next step in the investigation? > > Is the fact that migration/ram.c always does fflush after writing the EOS > have any relevance here? why does it do it, > and should s390 code also follow the same pattern? I didn't think it was required. And qemu_put_buffer loops if needed and calls qemu_fflush internally. It's possible here that the storage key code is just the canary - the first thing that detects that the stream is invalid after it all goes wrong. Dave > Thanks, > > Claudio > > > -- > Claudio Fontana > Engineering Manager Virtualization, SUSE Labs Core > > SUSE Software Solutions Italy Srl > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK