| Message ID | 20231017202633.296756-3-peterx@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | migration: Better error handling in rp thread, allow failures in recover | expand |
Peter Xu <peterx@redhat.com> wrote: > Normally the postcopy recover phase should only exist for a super short > period, that's the duration when QEMU is trying to recover from an > interrupted postcopy migration, during which handshake will be carried out > for continuing the procedure with state changes from PAUSED -> RECOVER -> > POSTCOPY_ACTIVE again. > > Here RECOVER phase should be super small, that happens right after the > admin specified a new but working network link for QEMU to reconnect to > dest QEMU. > > However there can still be case where the channel is broken in this small > RECOVER window. > > If it happens, with current code there's no way the src QEMU can got kicked > out of RECOVER stage. No way either to retry the recover in another channel > when established. > > This patch allows the RECOVER phase to fail itself too - we're mostly > ready, just some small things missing, e.g. properly kick the main > migration thread out when sleeping on rp_sem when we found that we're at > RECOVER stage. When this happens, it fails the RECOVER itself, and > rollback to PAUSED stage. Then the user can retry another round of > recovery. > > To make it even stronger, teach QMP command migrate-pause to explicitly > kick src/dst QEMU out when needed, so even if for some reason the migration > thread didn't got kicked out already by a failing rethrn-path thread, the > admin can also kick it out. > > This will be an super, super corner case, but still try to cover that. > > One can try to test this with two proxy channels for migration: > > (a) socat unix-listen:/tmp/src.sock,reuseaddr,fork tcp:localhost:10000 > (b) socat tcp-listen:10000,reuseaddr,fork unix:/tmp/dst.sock > > So the migration channel will be: > > (a) (b) > src -> /tmp/src.sock -> tcp:10000 -> /tmp/dst.sock -> dst > > Then to make QEMU hang at RECOVER stage, one can do below: > > (1) stop the postcopy using QMP command postcopy-pause > (2) kill the 2nd proxy (b) > (3) try to recover the postcopy using /tmp/src.sock on src > (4) src QEMU will go into RECOVER stage but won't be able to continue > from there, because the channel is actually broken at (b) > > Before this patch, step (4) will make src QEMU stuck in RECOVER stage, > without a way to kick the QEMU out or continue the postcopy again. After > this patch, (4) will quickly fail qemu and bounce back to PAUSED stage. > > Admin can also kick QEMU from (4) into PAUSED when needed using > migrate-pause when needed. > > After bouncing back to PAUSED stage, one can recover again. > > Reported-by: Xiaohui Li <xiaohli@redhat.com> > Reviewed-by: Fabiano Rosas <farosas@suse.de> > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2111332 > Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> > -void migration_rp_wait(MigrationState *s) > +int migration_rp_wait(MigrationState *s) > { > + /* If migration has failure already, ignore the wait */ > + if (migrate_has_error(s)) { > + return -1; > + } > + > qemu_sem_wait(&s->rp_state.rp_sem); > + > + /* After wait, double check that there's no failure */ > + if (migrate_has_error(s)) { > + return -1; > + } > + > + return 0; > } Shouldn't this be bool? We have (too many) functions in migration that returns 0/-1 and set an error, I think we should change them to return bool. Or even just test if err is set. Later, Juan.
On Tue, Oct 31, 2023 at 03:26:42PM +0100, Juan Quintela wrote: > > -void migration_rp_wait(MigrationState *s) > > +int migration_rp_wait(MigrationState *s) > > { > > + /* If migration has failure already, ignore the wait */ > > + if (migrate_has_error(s)) { > > + return -1; > > + } > > + > > qemu_sem_wait(&s->rp_state.rp_sem); > > + > > + /* After wait, double check that there's no failure */ > > + if (migrate_has_error(s)) { > > + return -1; > > + } > > + > > + return 0; > > } > > Shouldn't this be bool? > > We have (too many) functions in migration that returns 0/-1 and set an > error, I think we should change them to return bool. Or even just test > if err is set. Yeah this patch comes earlier than "switching to bools". I can make them bool after I rebase to the new pulls and see what's leftover. Thanks.
diff --git a/migration/migration.h b/migration/migration.h index 1d1ac13adb..0b695bbfb1 100644 --- a/migration/migration.h +++ b/migration/migration.h @@ -494,6 +494,7 @@ int migrate_init(MigrationState *s, Error **errp); bool migration_is_blocked(Error **errp); /* True if outgoing migration has entered postcopy phase */ bool migration_in_postcopy(void); +bool migration_postcopy_is_alive(int state); MigrationState *migrate_get_current(void); uint64_t ram_get_total_transferred_pages(void); @@ -534,8 +535,11 @@ void migration_populate_vfio_info(MigrationInfo *info); void migration_reset_vfio_bytes_transferred(void); void postcopy_temp_page_reset(PostcopyTmpPage *tmp_page); -/* Migration thread waiting for return path thread. */ -void migration_rp_wait(MigrationState *s); +/* + * Migration thread waiting for return path thread. Return non-zero if an + * error is detected. + */ +int migration_rp_wait(MigrationState *s); /* * Kick the migration thread waiting for return path messages. NOTE: the * name can be slightly confusing (when read as "kick the rp thread"), just diff --git a/migration/migration.c b/migration/migration.c index 3123c4a873..0661dad953 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -1348,6 +1348,17 @@ bool migration_in_postcopy(void) } } +bool migration_postcopy_is_alive(int state) +{ + switch (state) { + case MIGRATION_STATUS_POSTCOPY_ACTIVE: + case MIGRATION_STATUS_POSTCOPY_RECOVER: + return true; + default: + return false; + } +} + bool migration_in_postcopy_after_devices(MigrationState *s) { return migration_in_postcopy() && s->postcopy_after_devices; @@ -1557,8 +1568,15 @@ void qmp_migrate_pause(Error **errp) MigrationIncomingState *mis = migration_incoming_get_current(); int ret = 0; - if (ms->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) { + if (migration_postcopy_is_alive(ms->state)) { /* Source side, during postcopy */ + Error *error = NULL; + + /* Tell the core migration that we're pausing */ + error_setg(&error, "Postcopy migration is paused by the user"); + migrate_set_error(ms, error); + error_free(error); + qemu_mutex_lock(&ms->qemu_file_lock); if (ms->to_dst_file) { ret = qemu_file_shutdown(ms->to_dst_file); @@ -1567,10 +1585,17 @@ void qmp_migrate_pause(Error **errp) if (ret) { error_setg(errp, "Failed to pause source migration"); } + + /* + * Kick the migration thread out of any waiting windows (on behalf + * of the rp thread). + */ + migration_rp_kick(ms); + return; } - if (mis->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) { + if (migration_postcopy_is_alive(mis->state)) { ret = qemu_file_shutdown(mis->from_src_file); if (ret) { error_setg(errp, "Failed to pause destination migration"); @@ -1579,7 +1604,7 @@ void qmp_migrate_pause(Error **errp) } error_setg(errp, "migrate-pause is currently only supported " - "during postcopy-active state"); + "during postcopy-active or postcopy-recover state"); } bool migration_is_blocked(Error **errp) @@ -1754,9 +1779,21 @@ void qmp_migrate_continue(MigrationStatus state, Error **errp) qemu_sem_post(&s->pause_sem); } -void migration_rp_wait(MigrationState *s) +int migration_rp_wait(MigrationState *s) { + /* If migration has failure already, ignore the wait */ + if (migrate_has_error(s)) { + return -1; + } + qemu_sem_wait(&s->rp_state.rp_sem); + + /* After wait, double check that there's no failure */ + if (migrate_has_error(s)) { + return -1; + } + + return 0; } void migration_rp_kick(MigrationState *s) @@ -2018,6 +2055,20 @@ out: trace_source_return_path_thread_bad_end(); } + if (ms->state == MIGRATION_STATUS_POSTCOPY_RECOVER) { + /* + * this will be extremely unlikely: that we got yet another network + * issue during recovering of the 1st network failure.. during this + * period the main migration thread can be waiting on rp_sem for + * this thread to sync with the other side. + * + * When this happens, explicitly kick the migration thread out of + * RECOVER stage and back to PAUSED, so the admin can try + * everything again. + */ + migration_rp_kick(ms); + } + trace_source_return_path_thread_end(); rcu_unregister_thread(); @@ -2482,7 +2533,9 @@ static int postcopy_resume_handshake(MigrationState *s) qemu_savevm_send_postcopy_resume(s->to_dst_file); while (s->state == MIGRATION_STATUS_POSTCOPY_RECOVER) { - migration_rp_wait(s); + if (migration_rp_wait(s)) { + return -1; + } } if (s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) { diff --git a/migration/ram.c b/migration/ram.c index 544c5b63cf..973e872284 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -4175,7 +4175,9 @@ static int ram_dirty_bitmap_sync_all(MigrationState *s, RAMState *rs) /* Wait until all the ramblocks' dirty bitmap synced */ while (qatomic_read(&rs->postcopy_bmap_sync_requested)) { - migration_rp_wait(s); + if (migration_rp_wait(s)) { + return -1; + } } trace_ram_dirty_bitmap_sync_complete();
Normally the postcopy recover phase should only exist for a super short period, that's the duration when QEMU is trying to recover from an interrupted postcopy migration, during which handshake will be carried out for continuing the procedure with state changes from PAUSED -> RECOVER -> POSTCOPY_ACTIVE again. Here RECOVER phase should be super small, that happens right after the admin specified a new but working network link for QEMU to reconnect to dest QEMU. However there can still be case where the channel is broken in this small RECOVER window. If it happens, with current code there's no way the src QEMU can got kicked out of RECOVER stage. No way either to retry the recover in another channel when established. This patch allows the RECOVER phase to fail itself too - we're mostly ready, just some small things missing, e.g. properly kick the main migration thread out when sleeping on rp_sem when we found that we're at RECOVER stage. When this happens, it fails the RECOVER itself, and rollback to PAUSED stage. Then the user can retry another round of recovery. To make it even stronger, teach QMP command migrate-pause to explicitly kick src/dst QEMU out when needed, so even if for some reason the migration thread didn't got kicked out already by a failing rethrn-path thread, the admin can also kick it out. This will be an super, super corner case, but still try to cover that. One can try to test this with two proxy channels for migration: (a) socat unix-listen:/tmp/src.sock,reuseaddr,fork tcp:localhost:10000 (b) socat tcp-listen:10000,reuseaddr,fork unix:/tmp/dst.sock So the migration channel will be: (a) (b) src -> /tmp/src.sock -> tcp:10000 -> /tmp/dst.sock -> dst Then to make QEMU hang at RECOVER stage, one can do below: (1) stop the postcopy using QMP command postcopy-pause (2) kill the 2nd proxy (b) (3) try to recover the postcopy using /tmp/src.sock on src (4) src QEMU will go into RECOVER stage but won't be able to continue from there, because the channel is actually broken at (b) Before this patch, step (4) will make src QEMU stuck in RECOVER stage, without a way to kick the QEMU out or continue the postcopy again. After this patch, (4) will quickly fail qemu and bounce back to PAUSED stage. Admin can also kick QEMU from (4) into PAUSED when needed using migrate-pause when needed. After bouncing back to PAUSED stage, one can recover again. Reported-by: Xiaohui Li <xiaohli@redhat.com> Reviewed-by: Fabiano Rosas <farosas@suse.de> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2111332 Signed-off-by: Peter Xu <peterx@redhat.com> --- migration/migration.h | 8 ++++-- migration/migration.c | 63 +++++++++++++++++++++++++++++++++++++++---- migration/ram.c | 4 ++- 3 files changed, 67 insertions(+), 8 deletions(-)