Am 07.07.2015 um 15:09 hat Juan Quintela geschrieben:
> From: Li Zhijian <lizhij...@cn.fujitsu.com>
>
> Signed-off-by: Li Zhijian <lizhij...@cn.fujitsu.com>
> Signed-off-by: Wen Congyang <we...@cn.fujitsu.com>
> Signed-off-by: Juan Quintela <quint...@redhat.com>
> ---
> migration/ram.c | 23 +++++++++++++++++------
> 1 file changed, 17 insertions(+), 6 deletions(-)
In current master, HMP 'savevm' is broken (looks like a deadlock in RCU
code, it just hangs indefinitely). git bisect points to this patch.
The stack trace looks like this:
(gdb) thread apply all bt
Thread 3 (Thread 0x7f06febfe700 (LWP 5717)):
#0 0x00007f070e749f7d in __lll_lock_wait () from /lib64/libpthread.so.0
#1 0x00007f070e745d32 in _L_lock_791 () from /lib64/libpthread.so.0
#2 0x00007f070e745c38 in pthread_mutex_lock () from /lib64/libpthread.so.0
#3 0x00007f070fed8bc9 in qemu_mutex_lock (mutex=mutex@entry=0x7f07107e6700
<rcu_gp_lock>) at util/qemu-thread-posix.c:73
#4 0x00007f070fee7631 in synchronize_rcu () at util/rcu.c:129
#5 0x00007f070fee77d9 in call_rcu_thread (opaque=<optimized out>) at
util/rcu.c:240
#6 0x00007f070e743df5 in start_thread () from /lib64/libpthread.so.0
#7 0x00007f07066ab1ad in clone () from /lib64/libc.so.6
Thread 2 (Thread 0x7f06f940f700 (LWP 5719)):
#0 0x00007f070e749f7d in __lll_lock_wait () from /lib64/libpthread.so.0
#1 0x00007f070e74c4ec in _L_cond_lock_792 () from /lib64/libpthread.so.0
#2 0x00007f070e74c3c8 in __pthread_mutex_cond_lock () from
/lib64/libpthread.so.0
#3 0x00007f070e747795 in pthread_cond_wait@@GLIBC_2.3.2 () from
/lib64/libpthread.so.0
#4 0x00007f070fed8ca9 in qemu_cond_wait (cond=<optimized out>,
mutex=mutex@entry=0x7f07103b0400 <qemu_global_mutex>) at
util/qemu-thread-posix.c:132
#5 0x00007f070fc4daab in qemu_tcg_cpu_thread_fn (arg=<optimized out>) at
/home/kwolf/source/qemu/cpus.c:1050
#6 0x00007f070e743df5 in start_thread () from /lib64/libpthread.so.0
#7 0x00007f07066ab1ad in clone () from /lib64/libc.so.6
Thread 1 (Thread 0x7f070fb20bc0 (LWP 5716)):
#0 0x00007f07066a5949 in syscall () from /lib64/libc.so.6
#1 0x00007f070fed8fa2 in futex_wait (val=4294967295, ev=0x7f07107e66c0
<rcu_gp_event>) at util/qemu-thread-posix.c:301
#2 qemu_event_wait (ev=ev@entry=0x7f07107e66c0 <rcu_gp_event>) at
util/qemu-thread-posix.c:399
#3 0x00007f070fee7713 in wait_for_readers () at util/rcu.c:120
#4 synchronize_rcu () at util/rcu.c:149
#5 0x00007f070fc6e0c2 in migration_end () at
/home/kwolf/source/qemu/migration/ram.c:1033
#6 0x00007f070fc6ef23 in ram_save_complete (f=0x7f07122f9aa0,
opaque=<optimized out>) at /home/kwolf/source/qemu/migration/ram.c:1241
#7 0x00007f070fc71d75 in qemu_savevm_state_complete (f=f@entry=0x7f07122f9aa0)
at /home/kwolf/source/qemu/migration/savevm.c:836
#8 0x00007f070fc7298e in qemu_savevm_state (errp=0x7ffe2a081ff8,
f=0x7f07122f9aa0) at /home/kwolf/source/qemu/migration/savevm.c:945
#9 hmp_savevm (mon=0x7f071233b500, qdict=<optimized out>) at
/home/kwolf/source/qemu/migration/savevm.c:1353
#10 0x00007f070fc552d0 in handle_hmp_command (mon=mon@entry=0x7f071233b500,
cmdline=0x7f0712350197 "foo") at /home/kwolf/source/qemu/monitor.c:4058
#11 0x00007f070fc56467 in monitor_command_cb (opaque=0x7f071233b500,
cmdline=<optimized out>, readline_opaque=<optimized out>)
at /home/kwolf/source/qemu/monitor.c:5081
#12 0x00007f070fee6dbf in readline_handle_byte (rs=0x7f0712350190,
ch=<optimized out>) at util/readline.c:391
#13 0x00007f070fc55387 in monitor_read (opaque=<optimized out>, buf=<optimized
out>, size=<optimized out>) at /home/kwolf/source/qemu/monitor.c:5064
#14 0x00007f070fd17b21 in qemu_chr_be_write (len=<optimized out>,
buf=0x7ffe2a082640 "\n\331\367\325\001\200\377\377\200&\b*\376\177",
s=0x7f0712304670)
at qemu-char.c:306
#15 fd_chr_read (chan=<optimized out>, cond=<optimized out>,
opaque=0x7f0712304670) at qemu-char.c:1012
#16 0x00007f070e04c9ba in g_main_context_dispatch () from
/lib64/libglib-2.0.so.0
#17 0x00007f070fe61678 in glib_pollfds_poll () at main-loop.c:199
#18 os_host_main_loop_wait (timeout=<optimized out>) at main-loop.c:244
#19 main_loop_wait (nonblocking=<optimized out>) at main-loop.c:493
#20 0x00007f070fc24e9e in main_loop () at vl.c:1901
#21 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at
vl.c:4649
Kevin
> diff --git a/migration/ram.c b/migration/ram.c
> index 644f52a..9c0bcfe 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -494,6 +494,7 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t
> **current_data,
> return 1;
> }
>
> +/* Called with rcu_read_lock() to protect migration_bitmap */
> static inline
> ram_addr_t migration_bitmap_find_and_reset_dirty(MemoryRegion *mr,
> ram_addr_t start)
> @@ -502,26 +503,31 @@ ram_addr_t
> migration_bitmap_find_and_reset_dirty(MemoryRegion *mr,
> unsigned long nr = base + (start >> TARGET_PAGE_BITS);
> uint64_t mr_size = TARGET_PAGE_ALIGN(memory_region_size(mr));
> unsigned long size = base + (mr_size >> TARGET_PAGE_BITS);
> + unsigned long *bitmap;
>
> unsigned long next;
>
> + bitmap = atomic_rcu_read(&migration_bitmap);
> if (ram_bulk_stage && nr > base) {
> next = nr + 1;
> } else {
> - next = find_next_bit(migration_bitmap, size, nr);
> + next = find_next_bit(bitmap, size, nr);
> }
>
> if (next < size) {
> - clear_bit(next, migration_bitmap);
> + clear_bit(next, bitmap);
> migration_dirty_pages--;
> }
> return (next - base) << TARGET_PAGE_BITS;
> }
>
> +/* Called with rcu_read_lock() to protect migration_bitmap */
> static void migration_bitmap_sync_range(ram_addr_t start, ram_addr_t length)
> {
> + unsigned long *bitmap;
> + bitmap = atomic_rcu_read(&migration_bitmap);
> migration_dirty_pages +=
> - cpu_physical_memory_sync_dirty_bitmap(migration_bitmap, start,
> length);
> + cpu_physical_memory_sync_dirty_bitmap(bitmap, start, length);
> }
>
>
> @@ -1017,10 +1023,15 @@ void free_xbzrle_decoded_buf(void)
>
> static void migration_end(void)
> {
> - if (migration_bitmap) {
> + /* caller have hold iothread lock or is in a bh, so there is
> + * no writing race against this migration_bitmap
> + */
> + unsigned long *bitmap = migration_bitmap;
> + atomic_rcu_set(&migration_bitmap, NULL);
> + if (bitmap) {
> memory_global_dirty_log_stop();
> - g_free(migration_bitmap);
> - migration_bitmap = NULL;
> + synchronize_rcu();
> + g_free(bitmap);
> }
>
> XBZRLE_cache_lock();
> --
> 2.4.3
>
>
