[Qemu-devel] [PULL 08/21] migration: No need to take rcu during sync_dirty_bitmap

[Juan Quintela <quintela@redhat.com>]

From: Peter Xu <peterx@redhat.com>

cpu_physical_memory_sync_dirty_bitmap() has one RAMBlock* as
parameter, which means that it must be with RCU read lock held
already.  Taking it again inside seems redundant.  Removing it.
Instead comment on the functions about the RCU read lock.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20190603065056.25211-2-peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 include/exec/ram_addr.h | 5 +----
 migration/ram.c         | 1 +
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index f96777bb99..44dcc98de6 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -409,6 +409,7 @@ static inline void cpu_physical_memory_clear_dirty_range(ram_addr_t start,
 }
 
 
+/* Called with RCU critical section */
 static inline
 uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb,
                                                ram_addr_t start,
@@ -432,8 +433,6 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb,
                                         DIRTY_MEMORY_BLOCK_SIZE);
         unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
 
-        rcu_read_lock();
-
         src = atomic_rcu_read(
                 &ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION])->blocks;
 
@@ -453,8 +452,6 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb,
                 idx++;
             }
         }
-
-        rcu_read_unlock();
     } else {
         ram_addr_t offset = rb->offset;
 
diff --git a/migration/ram.c b/migration/ram.c
index 89eec7ee9d..48969db84b 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1674,6 +1674,7 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs,
     return ret;
 }
 
+/* Called with RCU critical section */
 static void migration_bitmap_sync_range(RAMState *rs, RAMBlock *rb,
                                         ram_addr_t length)
 {
-- 
2.21.0