Re: [PATCH 3/5] Migration thread mutex

Marcelo Tosatti
2011-08-29T18:40:49Z

On Sat, Aug 27, 2011 at 02:09:46PM -0400, Umesh Deshpande wrote:
> 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();
> + }

Dropping the iothread lock from within a timer handler is not safe.
This change to ram_save_live should be moved to the patch where
migration thread is introduced.