Re: [PATCH v2] migration: Fix blocking in POSTCOPY_DEVICE during package load

[Juraj Marcin <jmarcin@redhat.com>]

On 2026-04-23 15:14, Pranav Tyagi wrote:
> The package_loaded event is not set in case MIG_RP_MSG_PONG does not
> arrive on the source from the destination in the return path thread. The
> migration thread would then be blocked waiting for package_loaded event
> indefinitely in POSTCOPY_DEVICE state. Where as, in such a condition the
> source VM can safely resume as the destination has not yet started. The
> pong message can get lost in case of a network failure or destination
> crash before sending the pong.
> 
> This patch removes the package_loaded event and uses rp_sem, instead of
> kicking multiple events. The error is detected in case of network
> failure or destination crash and rp_sem is set in the out path of the
> return path thread. This will kick the migration thread out from a
> condition of indefinitely waiting for rp_sem. The migration thread then
> fails early and breaks from the migration loop to resume the vm on the
> source side.
> 
> Fixes: 7b842fe354c6 ("migration: Introduce POSTCOPY_DEVICE state")
> Signed-off-by: Pranav Tyagi <prtyagi@redhat.com>
> ---
> V1: https://lore.kernel.org/all/20260421052227.8278-1-prtyagi@redhat.com/
> 
> changed in v2:
> - removed postcopy_package_loaded_event and using rp_sem to kick the
>   migration thread
> - using migration_rp_wait() in place of qemu_event_wait() in the
>   migration thread
> 
>  migration/migration.c | 48 ++++++++++++++++++++++++++++---------------
>  migration/migration.h |  1 -
>  2 files changed, 31 insertions(+), 18 deletions(-)

Reviewed-by: Juraj Marcin <jmarcin@redhat.com>