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[Qemu-devel] [PATCH 5/9] exec: protect mru_block with RCU
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 5/9] exec: protect mru_block with RCU |
Date: |
Tue, 3 Feb 2015 13:52:24 +0100 |
Hence, freeing a RAMBlock has to be switched to call_rcu.
Signed-off-by: Paolo Bonzini <address@hidden>
---
exec.c | 60 +++++++++++++++++++++++++++++++++++---------------
include/exec/cpu-all.h | 2 ++
2 files changed, 44 insertions(+), 18 deletions(-)
diff --git a/exec.c b/exec.c
index a423def..05c5b44 100644
--- a/exec.c
+++ b/exec.c
@@ -811,7 +811,7 @@ static RAMBlock *qemu_get_ram_block(ram_addr_t addr)
RAMBlock *block;
/* The list is protected by the iothread lock here. */
- block = ram_list.mru_block;
+ block = atomic_rcu_read(&ram_list.mru_block);
if (block && addr - block->offset < block->max_length) {
goto found;
}
@@ -825,6 +825,22 @@ static RAMBlock *qemu_get_ram_block(ram_addr_t addr)
abort();
found:
+ /* It is safe to write mru_block outside the iothread lock. This
+ * is what happens:
+ *
+ * mru_block = xxx
+ * rcu_read_unlock()
+ * xxx removed from list
+ * rcu_read_lock()
+ * read mru_block
+ * mru_block = NULL;
+ * call_rcu(reclaim_ramblock, xxx);
+ * rcu_read_unlock()
+ *
+ * atomic_rcu_set is not needed here. The block was already published
+ * when it was placed into the list. Here we're just making an extra
+ * copy of the pointer.
+ */
ram_list.mru_block = block;
return block;
}
@@ -1381,14 +1397,16 @@ static ram_addr_t ram_block_add(RAMBlock *new_block,
Error **errp)
QTAILQ_INSERT_TAIL(&ram_list.blocks, new_block, next);
}
ram_list.mru_block = NULL;
+ atomic_rcu_set(&ram_list.version, ram_list.version + 1);
- ram_list.version++;
qemu_mutex_unlock_ramlist();
new_ram_size = last_ram_offset() >> TARGET_PAGE_BITS;
if (new_ram_size > old_ram_size) {
int i;
+
+ /* ram_list.dirty_memory[] is protected by the iothread lock. */
for (i = 0; i < DIRTY_MEMORY_NUM; i++) {
ram_list.dirty_memory[i] =
bitmap_zero_extend(ram_list.dirty_memory[i],
@@ -1525,14 +1543,32 @@ void qemu_ram_free_from_ptr(ram_addr_t addr)
if (addr == block->offset) {
QTAILQ_REMOVE(&ram_list.blocks, block, next);
ram_list.mru_block = NULL;
- ram_list.version++;
- g_free(block);
+ atomic_rcu_set(&ram_list.version, ram_list.version + 1);
+ call_rcu(block, (void (*)(struct RAMBlock *))g_free, rcu);
break;
}
}
qemu_mutex_unlock_ramlist();
}
+static void reclaim_ramblock(RAMBlock *block)
+{
+ if (block->flags & RAM_PREALLOC) {
+ ;
+ } else if (xen_enabled()) {
+ xen_invalidate_map_cache_entry(block->host);
+#ifndef _WIN32
+ } else if (block->fd >= 0) {
+ munmap(block->host, block->max_length);
+ close(block->fd);
+#endif
+ } else {
+ qemu_anon_ram_free(block->host, block->max_length);
+ }
+ g_free(block);
+}
+
+/* Called with the iothread lock held */
void qemu_ram_free(ram_addr_t addr)
{
RAMBlock *block;
@@ -1543,20 +1579,8 @@ void qemu_ram_free(ram_addr_t addr)
if (addr == block->offset) {
QTAILQ_REMOVE(&ram_list.blocks, block, next);
ram_list.mru_block = NULL;
- ram_list.version++;
- if (block->flags & RAM_PREALLOC) {
- ;
- } else if (xen_enabled()) {
- xen_invalidate_map_cache_entry(block->host);
-#ifndef _WIN32
- } else if (block->fd >= 0) {
- munmap(block->host, block->max_length);
- close(block->fd);
-#endif
- } else {
- qemu_anon_ram_free(block->host, block->max_length);
- }
- g_free(block);
+ atomic_rcu_set(&ram_list.version, ram_list.version + 1);
+ call_rcu(block, reclaim_ramblock, rcu);
break;
}
}
diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index 2c48286..b8781d1 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -24,6 +24,7 @@
#include "exec/memory.h"
#include "qemu/thread.h"
#include "qom/cpu.h"
+#include "qemu/rcu.h"
/* some important defines:
*
@@ -268,6 +269,7 @@ CPUArchState *cpu_copy(CPUArchState *env);
typedef struct RAMBlock RAMBlock;
struct RAMBlock {
+ struct rcu_head rcu;
struct MemoryRegion *mr;
uint8_t *host;
ram_addr_t offset;
--
1.8.3.1
[Qemu-devel] [PATCH 6/9] cosmetic changes preparing for the following patches, Paolo Bonzini, 2015/02/03