[Qemu-devel] [PATCH v2 4/5] rcu: Use automatic rc_read unlock in core memory/exec code

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Only in the cases where nothing else interesting happens
after the unlock.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 exec.c                  | 46 +++++++++++++----------------------------
 include/exec/ram_addr.h |  8 ++-----
 memory.c                | 15 +++++---------
 3 files changed, 21 insertions(+), 48 deletions(-)

diff --git a/exec.c b/exec.c
index 235d6bc883..ac3d933e1a 100644
--- a/exec.c
+++ b/exec.c
@@ -1034,16 +1034,14 @@ void tb_invalidate_phys_addr(AddressSpace *as, hwaddr addr, MemTxAttrs attrs)
         return;
     }
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     mr = address_space_translate(as, addr, &addr, &l, false, attrs);
     if (!(memory_region_is_ram(mr)
           || memory_region_is_romd(mr))) {
-        rcu_read_unlock();
         return;
     }
     ram_addr = memory_region_get_ram_addr(mr) + addr;
     tb_invalidate_phys_page_range(ram_addr, ram_addr + 1, 0);
-    rcu_read_unlock();
 }
 
 static void breakpoint_invalidate(CPUState *cpu, target_ulong pc)
@@ -1329,14 +1327,13 @@ static void tlb_reset_dirty_range_all(ram_addr_t start, ram_addr_t length)
     end = TARGET_PAGE_ALIGN(start + length);
     start &= TARGET_PAGE_MASK;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     block = qemu_get_ram_block(start);
     assert(block == qemu_get_ram_block(end - 1));
     start1 = (uintptr_t)ramblock_ptr(block, start - block->offset);
     CPU_FOREACH(cpu) {
         tlb_reset_dirty(cpu, start1, length);
     }
-    rcu_read_unlock();
 }
 
 /* Note: start and end must be within the same ram block.  */
@@ -1661,7 +1658,7 @@ void ram_block_dump(Monitor *mon)
     RAMBlock *block;
     char *psize;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     monitor_printf(mon, "%24s %8s  %18s %18s %18s\n",
                    "Block Name", "PSize", "Offset", "Used", "Total");
     RAMBLOCK_FOREACH(block) {
@@ -1673,7 +1670,6 @@ void ram_block_dump(Monitor *mon)
                        (uint64_t)block->max_length);
         g_free(psize);
     }
-    rcu_read_unlock();
 }
 
 #ifdef __linux__
@@ -1995,11 +1991,10 @@ static unsigned long last_ram_page(void)
     RAMBlock *block;
     ram_addr_t last = 0;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     RAMBLOCK_FOREACH(block) {
         last = MAX(last, block->offset + block->max_length);
     }
-    rcu_read_unlock();
     return last >> TARGET_PAGE_BITS;
 }
 
@@ -2086,7 +2081,7 @@ void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState *dev)
     }
     pstrcat(new_block->idstr, sizeof(new_block->idstr), name);
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     RAMBLOCK_FOREACH(block) {
         if (block != new_block &&
             !strcmp(block->idstr, new_block->idstr)) {
@@ -2095,7 +2090,6 @@ void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState *dev)
             abort();
         }
     }
-    rcu_read_unlock();
 }
 
 /* Called with iothread lock held.  */
@@ -2637,17 +2631,16 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
 
     if (xen_enabled()) {
         ram_addr_t ram_addr;
-        rcu_read_lock();
+        RCU_READ_LOCK_AUTO;
         ram_addr = xen_ram_addr_from_mapcache(ptr);
         block = qemu_get_ram_block(ram_addr);
         if (block) {
             *offset = ram_addr - block->offset;
         }
-        rcu_read_unlock();
         return block;
     }
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     block = atomic_rcu_read(&ram_list.mru_block);
     if (block && block->host && host - block->host < block->max_length) {
         goto found;
@@ -2663,7 +2656,6 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
         }
     }
 
-    rcu_read_unlock();
     return NULL;
 
 found:
@@ -2671,7 +2663,6 @@ found:
     if (round_offset) {
         *offset &= TARGET_PAGE_MASK;
     }
-    rcu_read_unlock();
     return block;
 }
 
@@ -3380,10 +3371,9 @@ MemTxResult address_space_read_full(AddressSpace *as, hwaddr addr,
     FlatView *fv;
 
     if (len > 0) {
-        rcu_read_lock();
+        RCU_READ_LOCK_AUTO;
         fv = address_space_to_flatview(as);
         result = flatview_read(fv, addr, attrs, buf, len);
-        rcu_read_unlock();
     }
 
     return result;
@@ -3397,10 +3387,9 @@ MemTxResult address_space_write(AddressSpace *as, hwaddr addr,
     FlatView *fv;
 
     if (len > 0) {
-        rcu_read_lock();
+        RCU_READ_LOCK_AUTO;
         fv = address_space_to_flatview(as);
         result = flatview_write(fv, addr, attrs, buf, len);
-        rcu_read_unlock();
     }
 
     return result;
@@ -3440,7 +3429,7 @@ static inline MemTxResult address_space_write_rom_internal(AddressSpace *as,
     hwaddr addr1;
     MemoryRegion *mr;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     while (len > 0) {
         l = len;
         mr = address_space_translate(as, addr, &addr1, &l, true, attrs);
@@ -3465,7 +3454,6 @@ static inline MemTxResult address_space_write_rom_internal(AddressSpace *as,
         buf += l;
         addr += l;
     }
-    rcu_read_unlock();
     return MEMTX_OK;
 }
 
@@ -3610,10 +3598,9 @@ bool address_space_access_valid(AddressSpace *as, hwaddr addr,
     FlatView *fv;
     bool result;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     fv = address_space_to_flatview(as);
     result = flatview_access_valid(fv, addr, len, is_write, attrs);
-    rcu_read_unlock();
     return result;
 }
 
@@ -3668,13 +3655,12 @@ void *address_space_map(AddressSpace *as,
     }
 
     l = len;
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     fv = address_space_to_flatview(as);
     mr = flatview_translate(fv, addr, &xlat, &l, is_write, attrs);
 
     if (!memory_access_is_direct(mr, is_write)) {
         if (atomic_xchg(&bounce.in_use, true)) {
-            rcu_read_unlock();
             return NULL;
         }
         /* Avoid unbounded allocations */
@@ -3690,7 +3676,6 @@ void *address_space_map(AddressSpace *as,
                                bounce.buffer, l);
         }
 
-        rcu_read_unlock();
         *plen = l;
         return bounce.buffer;
     }
@@ -3700,7 +3685,6 @@ void *address_space_map(AddressSpace *as,
     *plen = flatview_extend_translation(fv, addr, len, mr, xlat,
                                         l, is_write, attrs);
     ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen, true);
-    rcu_read_unlock();
 
     return ptr;
 }
@@ -3968,13 +3952,12 @@ bool cpu_physical_memory_is_io(hwaddr phys_addr)
     hwaddr l = 1;
     bool res;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     mr = address_space_translate(&address_space_memory,
                                  phys_addr, &phys_addr, &l, false,
                                  MEMTXATTRS_UNSPECIFIED);
 
     res = !(memory_region_is_ram(mr) || memory_region_is_romd(mr));
-    rcu_read_unlock();
     return res;
 }
 
@@ -3983,14 +3966,13 @@ int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque)
     RAMBlock *block;
     int ret = 0;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     RAMBLOCK_FOREACH(block) {
         ret = func(block, opaque);
         if (ret) {
             break;
         }
     }
-    rcu_read_unlock();
     return ret;
 }
 
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index a327a80cfe..38f3aaffbd 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -240,7 +240,7 @@ static inline bool cpu_physical_memory_all_dirty(ram_addr_t start,
     end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS;
     page = start >> TARGET_PAGE_BITS;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
 
     blocks = atomic_rcu_read(&ram_list.dirty_memory[client]);
 
@@ -262,8 +262,6 @@ static inline bool cpu_physical_memory_all_dirty(ram_addr_t start,
         base += DIRTY_MEMORY_BLOCK_SIZE;
     }
 
-    rcu_read_unlock();
-
     return dirty;
 }
 
@@ -315,13 +313,11 @@ static inline void cpu_physical_memory_set_dirty_flag(ram_addr_t addr,
     idx = page / DIRTY_MEMORY_BLOCK_SIZE;
     offset = page % DIRTY_MEMORY_BLOCK_SIZE;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
 
     blocks = atomic_rcu_read(&ram_list.dirty_memory[client]);
 
     set_bit_atomic(offset, blocks->blocks[idx]);
-
-    rcu_read_unlock();
 }
 
 static inline void cpu_physical_memory_set_dirty_range(ram_addr_t start,
diff --git a/memory.c b/memory.c
index 61a254c3f9..5bdde7cebb 100644
--- a/memory.c
+++ b/memory.c
@@ -799,14 +799,13 @@ FlatView *address_space_get_flatview(AddressSpace *as)
 {
     FlatView *view;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     do {
         view = address_space_to_flatview(as);
         /* If somebody has replaced as->current_map concurrently,
          * flatview_ref returns false.
          */
     } while (!flatview_ref(view));
-    rcu_read_unlock();
     return view;
 }
 
@@ -2177,12 +2176,11 @@ int memory_region_get_fd(MemoryRegion *mr)
 {
     int fd;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     while (mr->alias) {
         mr = mr->alias;
     }
     fd = mr->ram_block->fd;
-    rcu_read_unlock();
 
     return fd;
 }
@@ -2192,14 +2190,13 @@ void *memory_region_get_ram_ptr(MemoryRegion *mr)
     void *ptr;
     uint64_t offset = 0;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     while (mr->alias) {
         offset += mr->alias_offset;
         mr = mr->alias;
     }
     assert(mr->ram_block);
     ptr = qemu_map_ram_ptr(mr->ram_block, offset);
-    rcu_read_unlock();
 
     return ptr;
 }
@@ -2589,12 +2586,11 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
                                        hwaddr addr, uint64_t size)
 {
     MemoryRegionSection ret;
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     ret = memory_region_find_rcu(mr, addr, size);
     if (ret.mr) {
         memory_region_ref(ret.mr);
     }
-    rcu_read_unlock();
     return ret;
 }
 
@@ -2602,9 +2598,8 @@ bool memory_region_present(MemoryRegion *container, hwaddr addr)
 {
     MemoryRegion *mr;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_AUTO;
     mr = memory_region_find_rcu(container, addr, 1).mr;
-    rcu_read_unlock();
     return mr && mr != container;
 }
 
-- 
2.21.0