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authorDr. David Alan Gilbert <dgilbert@redhat.com>2019-09-13 17:35:07 +0100
committerDr. David Alan Gilbert <dgilbert@redhat.com>2019-09-25 15:51:19 +0100
commitd46a4847ca868aaf537df2b87ce07dcbcad6a224 (patch)
tree05605ee81a7c19d1ef22841d9350ed01902b71c4 /migration
parentde8434a35a7871f5f09ff1b22af2dad40a7a0fba (diff)
downloadqemu-arm-d46a4847ca868aaf537df2b87ce07dcbcad6a224.tar.gz
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 <dgilbert@redhat.com> Message-Id: <20190913163507.1403-3-dgilbert@redhat.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Diffstat (limited to 'migration')
-rw-r--r--migration/rdma.c39
1 files changed, 27 insertions, 12 deletions
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;
}