[PATCH v5 08/12] system/physmem: destroy ram block attributes before RCU-deferred reclaim

ram_block_attributes_destroy() was called from reclaim_ramblock(), which
runs as an RCU callback deferred by call_rcu().

However,when the RamDiscardManager is finalized, it will assert that its
source_list is empty in the next commit. Since the RCU callback hasn't
run yet, the source added by ram_block_attributes_create() is still
attached.

Move ram_block_attributes_destroy() into qemu_ram_free() so the source
is removed synchronously. This is safe because qemu_ram_free() during
shutdown runs after pause_all_vcpus(), so no vCPU thread can
concurrently access the attributes via kvm_convert_memory().

Reviewed-by: Peter Xu <[email protected]>
Signed-off-by: Marc-André Lureau <[email protected]>
---
 system/physmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/system/physmem.c b/system/physmem.c
index 7bcbf875736..ddb67ba2359 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2583,7 +2583,6 @@ static void reclaim_ramblock(RAMBlock *block)
     }
 
     if (block->guest_memfd >= 0) {
-        ram_block_attributes_destroy(block->attributes);
         close(block->guest_memfd);
         ram_block_coordinated_discard_require(false);
     }
@@ -2612,6 +2611,7 @@ void qemu_ram_free(RAMBlock *block)
     /* Write list before version */
     smp_wmb();
     ram_list.version++;
+    g_clear_pointer(&block->attributes, ram_block_attributes_destroy);
     call_rcu(block, reclaim_ramblock, rcu);
     qemu_mutex_unlock_ramlist();
 }

-- 
2.54.0