From 4ce56229087860805877075ddb29dd44578365a9 Mon Sep 17 00:00:00 2001 From: Fabiano Rosas Date: Tue, 17 Sep 2024 15:58:02 -0300 Subject: migration/multifd: Fix rb->receivedmap cleanup race Fix a segmentation fault in multifd when rb->receivedmap is cleared too early. After commit 5ef7e26bdb ("migration/multifd: solve zero page causing multiple page faults"), multifd started using the rb->receivedmap bitmap, which belongs to ram.c and is initialized and *freed* from the ram SaveVMHandlers. Multifd threads are live until migration_incoming_state_destroy(), which is called after qemu_loadvm_state_cleanup(), leading to a crash when accessing rb->receivedmap. process_incoming_migration_co() ... qemu_loadvm_state() multifd_nocomp_recv() qemu_loadvm_state_cleanup() ramblock_recv_bitmap_set_offset() rb->receivedmap = NULL set_bit_atomic(..., rb->receivedmap) ... migration_incoming_state_destroy() multifd_recv_cleanup() multifd_recv_terminate_threads(NULL) Move the loadvm cleanup into migration_incoming_state_destroy(), after multifd_recv_cleanup() to ensure multifd threads have already exited when rb->receivedmap is cleared. Adjust the postcopy listen thread comment to indicate that we still want to skip the cpu synchronization. CC: qemu-stable@nongnu.org Fixes: 5ef7e26bdb ("migration/multifd: solve zero page causing multiple page faults") Signed-off-by: Fabiano Rosas Link: https://lore.kernel.org/r/20240917185802.15619-3-farosas@suse.de [peterx: added comment in migration_incoming_state_destroy()] Signed-off-by: Peter Xu --- migration/migration.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'migration/migration.c') diff --git a/migration/migration.c b/migration/migration.c index 3dea06d577..ae2be31557 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -378,6 +378,11 @@ void migration_incoming_state_destroy(void) struct MigrationIncomingState *mis = migration_incoming_get_current(); multifd_recv_cleanup(); + /* + * RAM state cleanup needs to happen after multifd cleanup, because + * multifd threads can use some of its states (receivedmap). + */ + qemu_loadvm_state_cleanup(); if (mis->to_src_file) { /* Tell source that we are done */ -- cgit 1.4.1