[PATCH 3/5] Migration thread mutex

Umesh Deshpande
2011-08-27T18:09:46Z

This patch implements migrate_ram mutex, which protects the RAMBlock list
traversal in the migration thread during the transfer of a ram from their
addition/removal from the iothread.

Note: Combination of iothread mutex and migration thread mutex works as a
rw-lock. Both mutexes are acquired while modifying the ram_list members or RAM
block list.

Signed-off-by: Umesh Deshpande <udeshpan@redhat.com>
---
arch_init.c | 21 +++++++++++++++++++++
cpu-all.h | 3 +++
exec.c | 23 +++++++++++++++++++++++
qemu-common.h | 2 ++
4 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index 484b39d..9d02270 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -109,6 +109,7 @@ static int is_dup_page(uint8_t *page, uint8_t ch)

static RAMBlock *last_block;
static ram_addr_t last_offset;
+static uint64_t last_version;

static int ram_save_block(QEMUFile *f)
{
@@ -170,6 +171,7 @@ static int ram_save_block(QEMUFile *f)

last_block = block;
last_offset = offset;
+ last_version = ram_list.version;

return bytes_sent;
}
@@ -270,6 +272,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
bytes_transferred = 0;
last_block = NULL;
last_offset = 0;
+ last_version = ram_list.version = 0;
sort_ram_list();

/* Make sure all dirty bits are set */
@@ -298,6 +301,17 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
bytes_transferred_last = bytes_transferred;
bwidth = qemu_get_clock_ns(rt_clock);

+ if (stage != 3) {
+ qemu_mutex_lock_migrate_ram();
+ qemu_mutex_unlock_iothread();
+ }
+
+ if (ram_list.version != last_version) {
+ /* RAM block added or removed */
+ last_block = NULL;
+ last_offset = 0;
+ }
+
while (!qemu_file_rate_limit(f)) {
int bytes_sent;

@@ -308,6 +322,13 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
}
}

+ if (stage != 3) {
+ qemu_mutex_unlock_migrate_ram();
+ qemu_mutex_lock_iothread();
+ /* Lock ordering : iothread mutex is always acquired outside migrate_ram
+ * mutex critical section to avoid deadlock */
+ }
+
bwidth = qemu_get_clock_ns(rt_clock) - bwidth;
bwidth = (bytes_transferred - bytes_transferred_last) / bwidth;

diff --git a/cpu-all.h b/cpu-all.h
index 6b217a2..b85483f 100644
--- a/cpu-all.h
+++ b/cpu-all.h
@@ -21,6 +21,7 @@

#include "qemu-common.h"
#include "cpu-common.h"
+#include "qemu-thread.h"

/* some important defines:
*
@@ -932,7 +933,9 @@ typedef struct RAMBlock {
} RAMBlock;

typedef struct RAMList {
+ QemuMutex mutex; /* Protects RAM block list */
uint8_t *phys_dirty;
+ uint32_t version; /* To detect ram block addition/removal */
QLIST_HEAD(ram, RAMBlock) blocks;
QLIST_HEAD(, RAMBlock) blocks_mru;
} RAMList;
diff --git a/exec.c b/exec.c
index c5c247c..7627483 100644
--- a/exec.c
+++ b/exec.c
@@ -582,6 +582,7 @@ void cpu_exec_init_all(unsigned long tb_size)
code_gen_alloc(tb_size);
code_gen_ptr = code_gen_buffer;
page_init();
+ qemu_mutex_init(&ram_list.mutex);
#if !defined(CONFIG_USER_ONLY)
io_mem_init();
#endif
@@ -2802,6 +2803,16 @@ static long gethugepagesize(const char *path)
return fs.f_bsize;
}

+void qemu_mutex_lock_migrate_ram(void)
+{
+ qemu_mutex_lock(&ram_list.mutex);
+}
+
+void qemu_mutex_unlock_migrate_ram(void)
+{
+ qemu_mutex_unlock(&ram_list.mutex);
+}
+
static void *file_ram_alloc(RAMBlock *block,
ram_addr_t memory,
const char *path)
@@ -2976,14 +2987,20 @@ ram_addr_t qemu_ram_alloc_from_ptr(DeviceState *dev, const char *name,
}
new_block->length = size;

+ qemu_mutex_lock_migrate_ram();
+
QLIST_INSERT_HEAD(&ram_list.blocks, new_block, next);
QLIST_INSERT_HEAD(&ram_list.blocks_mru, new_block, next_mru);

+ ram_list.version++;
+
ram_list.phys_dirty = qemu_realloc(ram_list.phys_dirty,
last_ram_offset() >> TARGET_PAGE_BITS);
memset(ram_list.phys_dirty + (new_block->offset >> TARGET_PAGE_BITS),
0xff, size >> TARGET_PAGE_BITS);

+ qemu_mutex_unlock_migrate_ram();
+
if (kvm_enabled())
kvm_setup_guest_memory(new_block->host, size);

@@ -3001,8 +3018,11 @@ void qemu_ram_free_from_ptr(ram_addr_t addr)

QLIST_FOREACH(block, &ram_list.blocks, next) {
if (addr == block->offset) {
+ qemu_mutex_lock_migrate_ram();
QLIST_REMOVE(block, next);
QLIST_REMOVE(block, next_mru);
+ ram_list.version++;
+ qemu_mutex_unlock_migrate_ram();
qemu_free(block);
return;
}
@@ -3015,8 +3035,11 @@ void qemu_ram_free(ram_addr_t addr)

QLIST_FOREACH(block, &ram_list.blocks, next) {
if (addr == block->offset) {
+ qemu_mutex_lock_migrate_ram();
QLIST_REMOVE(block, next);
QLIST_REMOVE(block, next_mru);
+ ram_list.version++;
+ qemu_mutex_unlock_migrate_ram();
if (block->flags & RAM_PREALLOC_MASK) {
;
} else if (mem_path) {
diff --git a/qemu-common.h b/qemu-common.h
index abd7a75..7dabfe9 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -212,6 +212,8 @@ char *qemu_strndup(const char *str, size_t size);

void qemu_mutex_lock_iothread(void);
void qemu_mutex_unlock_iothread(void);
+void qemu_mutex_lock_migrate_ram(void);
+void qemu_mutex_unlock_migrate_ram(void);

int qemu_open(const char *name, int flags, ...);
ssize_t qemu_write_full(int fd, const void *buf, size_t count)
--
1.7.4.1