From d46a4847ca868aaf537df2b87ce07dcbcad6a224 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Fri, 13 Sep 2019 17:35:07 +0100 Subject: migration/rdma.c: Swap synchronize_rcu for call_rcu This fixes a deadlock that can occur on the migration source after a failed RDMA migration; as the source tries to cleanup it clears a pair of pointers and uses synchronize_rcu to wait; this is happening on the main thread. With the CPUs running a CPU thread can be an rcu reader and attempt to grab the main lock (kvm_handle_io->address_space_write->flatview_write->flatview_write_continue-> prepare_mmio_access->qemu_mutex_lock_iothread_impl) Replace the synchronize_rcu with a call_rcu to postpone the freeing. Fixes: 74637e6f08fceda98806 ("migration: implement bi-directional RDMA QIOChannel") ( https://bugzilla.redhat.com/show_bug.cgi?id=1746787 ) Signed-off-by: Dr. David Alan Gilbert Message-Id: <20190913163507.1403-3-dgilbert@redhat.com> Reviewed-by: Peter Xu Signed-off-by: Dr. David Alan Gilbert --- migration/rdma.c | 39 +++++++++++++++++++++++++++------------ 1 file changed, 27 insertions(+), 12 deletions(-) (limited to 'migration') diff --git a/migration/rdma.c b/migration/rdma.c index 0fcf02f48e..4c74e88a37 100644 --- a/migration/rdma.c +++ b/migration/rdma.c @@ -3017,11 +3017,35 @@ static void qio_channel_rdma_set_aio_fd_handler(QIOChannel *ioc, } } +struct rdma_close_rcu { + struct rcu_head rcu; + RDMAContext *rdmain; + RDMAContext *rdmaout; +}; + +/* callback from qio_channel_rdma_close via call_rcu */ +static void qio_channel_rdma_close_rcu(struct rdma_close_rcu *rcu) +{ + if (rcu->rdmain) { + qemu_rdma_cleanup(rcu->rdmain); + } + + if (rcu->rdmaout) { + qemu_rdma_cleanup(rcu->rdmaout); + } + + g_free(rcu->rdmain); + g_free(rcu->rdmaout); + g_free(rcu); +} + static int qio_channel_rdma_close(QIOChannel *ioc, Error **errp) { QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(ioc); RDMAContext *rdmain, *rdmaout; + struct rdma_close_rcu *rcu = g_new(struct rdma_close_rcu, 1); + trace_qemu_rdma_close(); rdmain = rioc->rdmain; @@ -3034,18 +3058,9 @@ static int qio_channel_rdma_close(QIOChannel *ioc, atomic_rcu_set(&rioc->rdmaout, NULL); } - synchronize_rcu(); - - if (rdmain) { - qemu_rdma_cleanup(rdmain); - } - - if (rdmaout) { - qemu_rdma_cleanup(rdmaout); - } - - g_free(rdmain); - g_free(rdmaout); + rcu->rdmain = rdmain; + rcu->rdmaout = rdmaout; + call_rcu(rcu, qio_channel_rdma_close_rcu, rcu); return 0; } -- cgit v1.2.3