Commit dd4fe8844b changed the reporting of expected downtime behavior, so that the value will be calculated on-demand. One side effect on the change is QEMU will allow the calculation to happen anytime even if there's no transfer happening for a short while.
PeterM reported an ubsan report from clang when running migration-test with aarch64 binary on x86_64 hosts. I can also reproduce if I run the test concurrently so some of the src QEMU may not get chance to push any data, causing mbps to be 0: ../migration/migration.c:1051:12: runtime error: -nan is outside the range of representable values of type 'long' Fix it by properly handle both Inf and Nan to return INT64_MAX. Add a rich comment, per PeterM's suggestion. Link: https://lore.kernel.org/r/CAFEAcA-MYH6C39xO0OLx4-M5pKurJpurwRsMqZe9q=w-nsh...@mail.gmail.com Reported-by: Peter Maydell <[email protected]> Fixes: dd4fe8844b ("migration: Calculate expected downtime on demand") Signed-off-by: Peter Xu <[email protected]> --- migration/migration.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/migration/migration.c b/migration/migration.c index b6f78eb3ac..05f10e4576 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -63,6 +63,7 @@ #include "system/dirtylimit.h" #include "qemu/sockets.h" #include "system/kvm.h" +#include "math.h" #define NOTIFIER_ELEM_INIT(array, elem) \ [elem] = NOTIFIER_WITH_RETURN_LIST_INITIALIZER((array)[elem]) @@ -1044,12 +1045,29 @@ static bool migrate_show_downtime(MigrationState *s) /* Return expected downtime (unit: milliseconds) */ int64_t migration_downtime_calc_expected(MigrationState *s) { + double expected_ms; + if (mig_stats.dirty_sync_count <= 1) { return migrate_downtime_limit(); } - return mig_stats.dirty_bytes_last_sync / + expected_ms = mig_stats.dirty_bytes_last_sync / migration_get_switchover_bw(s) * 1000; + + /* + * If we haven't been able to transfer any data, the result here could + * be NaN (for 0 / 0) or infinity (something else / 0). + * + * Return INT64_MAX as our best approximation to "this will take + * forever to complete". If the problem is transient (e.g. we just + * haven't started to transfer yet) we'll recalculate to a more + * accurate figure later. + */ + if (isnan(expected_ms) || expected_ms >= (double)INT64_MAX) { + return INT64_MAX; + } + + return (int64_t) expected_ms; } static void populate_time_info(MigrationInfo *info, MigrationState *s) -- 2.53.0
