Re: [Qemu-devel] [RFC PATCH] migration: do not use atomic__nocheck() functions directly

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

* Philippe Mathieu-Daudé (f4bug@amsat.org) wrote:
> (incorrectly use in 3be98be4e9f)
> 
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

I'm a bit confused; isnt the only difference between the nocheck
versions that it'll fail at compile time instead of link?

Dave

> ---
> currently on ppc32 the linking fails:
> 
>   CC      migration/postcopy-ram.o
> ...
>   LINK    microblaze-softmmu/qemu-system-microblaze
> ../migration/postcopy-ram.o: In function `mark_postcopy_blocktime_end':
> migration/postcopy-ram.c:717: undefined reference to `__atomic_fetch_add_8'
> migration/postcopy-ram.c:738: undefined reference to `__atomic_fetch_add_8'
> ../migration/postcopy-ram.o: In function `mark_postcopy_blocktime_begin':
> migration/postcopy-ram.c:651: undefined reference to `__atomic_exchange_8'
> migration/postcopy-ram.c:652: undefined reference to `__atomic_exchange_8'
> migration/postcopy-ram.c:661: undefined reference to `__atomic_exchange_8'
> collect2: error: ld returned 1 exit status
> Makefile:193: recipe for target 'qemu-system-microblaze' failed
> make[1]: *** [qemu-system-microblaze] Error 1
> 
> with this patch the compilation fails:
> 
>   CC      migration/postcopy-ram.o
> In file included from include/qemu/osdep.h:36:0,
>                  from migration/postcopy-ram.c:19:
> migration/postcopy-ram.c: In function 'mark_postcopy_blocktime_begin':
> include/qemu/compiler.h:86:30: error: static assertion failed: "not expecting: sizeof(*&dc->last_begin) > ATOMIC_REG_SIZE"
>  #define QEMU_BUILD_BUG_ON(x) _Static_assert(!(x), "not expecting: " #x)
>                               ^
> include/qemu/atomic.h:183:5: note: in expansion of macro 'QEMU_BUILD_BUG_ON'
>      QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE);      \
>      ^
> migration/postcopy-ram.c:651:5: note: in expansion of macro 'atomic_xchg'
>      atomic_xchg(&dc->last_begin, now_ms);
>      ^
> 
>  migration/postcopy-ram.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 7814da5b4b..6ecc1aa820 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -648,17 +648,17 @@ static void mark_postcopy_blocktime_begin(uintptr_t addr, uint32_t ptid,
>          atomic_inc(&dc->smp_cpus_down);
>      }
>  
> -    atomic_xchg__nocheck(&dc->last_begin, now_ms);
> -    atomic_xchg__nocheck(&dc->page_fault_vcpu_time[cpu], now_ms);
> -    atomic_xchg__nocheck(&dc->vcpu_addr[cpu], addr);
> +    atomic_xchg(&dc->last_begin, now_ms);
> +    atomic_xchg(&dc->page_fault_vcpu_time[cpu], now_ms);
> +    atomic_xchg(&dc->vcpu_addr[cpu], addr);
>  
>      /* check it here, not at the begining of the function,
>       * due to, check could accur early than bitmap_set in
>       * qemu_ufd_copy_ioctl */
>      already_received = ramblock_recv_bitmap_test(rb, (void *)addr);
>      if (already_received) {
> -        atomic_xchg__nocheck(&dc->vcpu_addr[cpu], 0);
> -        atomic_xchg__nocheck(&dc->page_fault_vcpu_time[cpu], 0);
> +        atomic_xchg(&dc->vcpu_addr[cpu], 0);
> +        atomic_xchg(&dc->page_fault_vcpu_time[cpu], 0);
>          atomic_dec(&dc->smp_cpus_down);
>      }
>      trace_mark_postcopy_blocktime_begin(addr, dc, dc->page_fault_vcpu_time[cpu],
> @@ -719,7 +719,7 @@ static void mark_postcopy_blocktime_end(uintptr_t addr)
>              read_vcpu_time == 0) {
>              continue;
>          }
> -        atomic_xchg__nocheck(&dc->vcpu_addr[i], 0);
> +        atomic_xchg(&dc->vcpu_addr[i], 0);
>          vcpu_blocktime = now_ms - read_vcpu_time;
>          affected_cpu += 1;
>          /* we need to know is that mark_postcopy_end was due to
> -- 
> 2.15.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK