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c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1726599489; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LbLygEtJVaBxRuqfrAcm5XUtKM9vMfxUGYr2q5ibimI=; b=C8I6jADYs8IzIkzKedjpoPfUgz3WB1udg6BCY6a6K2ov4tYu83HKq6DFj+xrk5OHFztQ0I GxwRef+I/9mphZDg== From: Fabiano Rosas To: qemu-devel@nongnu.org Cc: Peter Xu , Peter Maydell , qemu-stable@nongnu.org Subject: [PATCH 2/2] migration/multifd: Fix rb->receivedmap cleanup race Date: Tue, 17 Sep 2024 15:58:02 -0300 Message-Id: <20240917185802.15619-3-farosas@suse.de> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20240917185802.15619-1-farosas@suse.de> References: <20240917185802.15619-1-farosas@suse.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[99.99%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; 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charset="utf-8" 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 =3D NULL set_bit_atomic(..., rb->receiv= edmap) ... 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 pag= e faults") Signed-off-by: Fabiano Rosas Reviewed-by: Peter Xu --- migration/migration.c | 1 + migration/savevm.c | 6 ++++-- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/migration/migration.c b/migration/migration.c index 3dea06d577..b190a574b1 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -378,6 +378,7 @@ void migration_incoming_state_destroy(void) struct MigrationIncomingState *mis =3D migration_incoming_get_current(= ); =20 multifd_recv_cleanup(); + qemu_loadvm_state_cleanup(); =20 if (mis->to_src_file) { /* Tell source that we are done */ diff --git a/migration/savevm.c b/migration/savevm.c index d0759694fd..7e1e27182a 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -2979,7 +2979,10 @@ int qemu_loadvm_state(QEMUFile *f) trace_qemu_loadvm_state_post_main(ret); =20 if (mis->have_listen_thread) { - /* Listen thread still going, can't clean up yet */ + /* + * Postcopy listen thread still going, don't synchronize the + * cpus yet. + */ return ret; } =20 @@ -3022,7 +3025,6 @@ int qemu_loadvm_state(QEMUFile *f) } } =20 - qemu_loadvm_state_cleanup(); cpu_synchronize_all_post_init(); =20 return ret; --=20 2.35.3