Re: [Qemu-devel] [RFC PATCH V7 07/19] protect TBContext with tb_lock.

[Frederic Konrad]

On 10/08/2015 17:27, address@hidden wrote:
> From: KONRAD Frederic <address@hidden>
>
> This protects TBContext with tb_lock to make tb_* thread safe.
>
> We can still have issue with tb_flush in case of multithread TCG:
>    An other CPU can be executing code during a flush.
>
> This can be fixed later by making all other TCG thread exiting before calling
> tb_flush().
>
> tb_find_slow is separated into tb_find_slow and tb_find_physical as the whole
> tb_find_slow doesn't require to lock the tb.
>
> Signed-off-by: KONRAD Frederic <address@hidden>
>
> Changes:
[...]
>   
> @@ -675,6 +710,7 @@ static inline void code_gen_alloc(size_t tb_size)
>               CODE_GEN_AVG_BLOCK_SIZE;
>       tcg_ctx.tb_ctx.tbs =
>               g_malloc(tcg_ctx.code_gen_max_blocks * sizeof(TranslationBlock));
> +    qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock);
>   }
>   
>   /* Must be called before using the QEMU cpus. 'tb_size' is the size
> @@ -699,16 +735,22 @@ bool tcg_enabled(void)
>       return tcg_ctx.code_gen_buffer != NULL;
>   }
>   
> -/* Allocate a new translation block. Flush the translation buffer if
> -   too many translation blocks or too much generated code. */
> +/*
> + * Allocate a new translation block. Flush the translation buffer if
> + * too many translation blocks or too much generated code.
> + * tb_alloc is not thread safe but tb_gen_code is protected by a mutex so this
> + * function is called only by one thread.
> + */
>   static TranslationBlock *tb_alloc(target_ulong pc)
>   {
> -    TranslationBlock *tb;
> +    TranslationBlock *tb = NULL;
>   
>       if (tcg_ctx.tb_ctx.nb_tbs >= tcg_ctx.code_gen_max_blocks ||
>           (tcg_ctx.code_gen_ptr - tcg_ctx.code_gen_buffer) >=
>            tcg_ctx.code_gen_buffer_max_size) {
> -        return NULL;
> +        tb = &tcg_ctx.tb_ctx.tbs[tcg_ctx.tb_ctx.nb_tbs++];
> +        tb->pc = pc;
> +        tb->cflags = 0;

Missed this wrong unreverted part which in the end doesn't do a tb_flush 
when required and crashes!
Fixing that allows me to boot with jessie and virt.

Fred