* Christian Borntraeger (borntrae...@de.ibm.com) wrote:
> On 04/26/2017 08:37 PM, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> >
> > When an all-zero page is received during the precopy
> > phase of a postcopy-enabled migration we must force
> > allocation otherwise accesses to the page will still
> > get blocked by userfault.
> >
> > Symptom:
> > a) If the page is accessed by a device during device-load
> > then we get a deadlock as the source finishes sending
> > all its pages but the destination device-load is still
> > paused and so doesn't clean up.
> >
> > b) If the page is accessed later, then the thread will stay
> > paused until the end of migration rather than carrying on
> > running, until we release userfault at the end.
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> > Reported-by: Christian Borntraeger <borntrae...@de.ibm.com>
>
> CC stable? after all the guest hangs on both sides
>
> Has survived 40 migrations (usually failed at the 2nd)
> Tested-by: Christian Borntraeger <borntrae...@de.ibm.com>
Great...but.....
Andrea (added to the mail) says this shouldn't be necessary.
The read we were doing in the is_zero_range() should have been sufficient
to get the page mapped and that zero page should have survived.
So - I guess that's back a step, we need to figure out why the
page disapepars for you.
Dave
>
> > ---
> > include/migration/migration.h | 3 ++-
> > migration/ram.c | 12 ++++++++----
> > migration/rdma.c | 2 +-
> > 3 files changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index ba1a16cbc1..b47904033c 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -265,7 +265,8 @@ uint64_t xbzrle_mig_pages_overflow(void);
> > uint64_t xbzrle_mig_pages_cache_miss(void);
> > double xbzrle_mig_cache_miss_rate(void);
> >
> > -void ram_handle_compressed(void *host, uint8_t ch, uint64_t size);
> > +void ram_handle_compressed(void *host, uint8_t ch, uint64_t size,
> > + bool always_write);
> > void ram_debug_dump_bitmap(unsigned long *todump, bool expected);
> > /* For outgoing discard bitmap */
> > int ram_postcopy_send_discard_bitmap(MigrationState *ms);
> > diff --git a/migration/ram.c b/migration/ram.c
> > index f48664ec62..b4ed41c725 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -2274,10 +2274,12 @@ static inline void
> > *host_from_ram_block_offset(RAMBlock *block,
> > * @host: host address for the zero page
> > * @ch: what the page is filled from. We only support zero
> > * @size: size of the zero page
> > + * @always_write: Always perform the memset even if it's zero
> > */
> > -void ram_handle_compressed(void *host, uint8_t ch, uint64_t size)
> > +void ram_handle_compressed(void *host, uint8_t ch, uint64_t size,
> > + bool always_write)
> > {
> > - if (ch != 0 || !is_zero_range(host, size)) {
> > + if (ch != 0 || always_write || !is_zero_range(host, size)) {
> > memset(host, ch, size);
> > }
> > }
> > @@ -2514,7 +2516,8 @@ static int ram_load_postcopy(QEMUFile *f)
> > switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
> > case RAM_SAVE_FLAG_COMPRESS:
> > ch = qemu_get_byte(f);
> > - memset(page_buffer, ch, TARGET_PAGE_SIZE);
> > + ram_handle_compressed(page_buffer, ch, TARGET_PAGE_SIZE,
> > + true);
> > if (ch) {
> > all_zero = false;
> > }
> > @@ -2664,7 +2667,8 @@ static int ram_load(QEMUFile *f, void *opaque, int
> > version_id)
> >
> > case RAM_SAVE_FLAG_COMPRESS:
> > ch = qemu_get_byte(f);
> > - ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
> > + ram_handle_compressed(host, ch, TARGET_PAGE_SIZE,
> > + postcopy_advised);
> > break;
> >
> > case RAM_SAVE_FLAG_PAGE:
> > diff --git a/migration/rdma.c b/migration/rdma.c
> > index fe0a4b5a83..07a9bd75d8 100644
> > --- a/migration/rdma.c
> > +++ b/migration/rdma.c
> > @@ -3164,7 +3164,7 @@ static int qemu_rdma_registration_handle(QEMUFile *f,
> > void *opaque)
> > host_addr = block->local_host_addr +
> > (comp->offset - block->offset);
> >
> > - ram_handle_compressed(host_addr, comp->value, comp->length);
> > + ram_handle_compressed(host_addr, comp->value, comp->length,
> > false);
> > break;
> >
> > case RDMA_CONTROL_REGISTER_FINISHED:
> >
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
