Re: [Qemu-devel] [PATCH v2 2/6] exec: don't use cpu_index to detect if cpu_exec_init()'s been called for cpu

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Jul 25, 2016 at 11:59:20AM +0200, Igor Mammedov wrote:
> Instead use QTAIL's tqe_prev field to detect if cpu's been
> placed in list by cpu_exec_init() which is always set if
> QTAIL element is in list.
> 
> Fixes SIGSEGV on failure path in case cpu_index is assigned
> by board and cpu.relalize() fails before cpu_exec_init() is called.
> 
> In follow up patches, cpu_index will be assigned by boards that
> support cpu hot(un)plug and need stable cpu_index that doesn't
> depend on order cpus are created/removed.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Reported-by: David Gibson <david@gibson.dropbear.id.au>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> v2:
>   replace setting tqe_prev to NULL in generic QTAIL_REMOVE
>   with a check and cleanup in cpu_exec_exit() to be on safe side.
>   And delay QTAIL_REMOVE() change to 2.8.
> ---
>  exec.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 2f57c62..ae45a70 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -643,13 +643,14 @@ void cpu_exec_exit(CPUState *cpu)
>      CPUClass *cc = CPU_GET_CLASS(cpu);
>  
>      cpu_list_lock();
> -    if (cpu->cpu_index == -1) {
> -        /* cpu_index was never allocated by this @cpu or was already freed. */
> +    if (cpu->node.tqe_prev == NULL) {
> +        /* there is nothing to undo since cpu_exec_init() hasn't been called */
>          cpu_list_unlock();
>          return;
>      }
>  
>      QTAILQ_REMOVE(&cpus, cpu, node);
> +    cpu->node.tqe_prev = NULL;
>      cpu_release_index(cpu);
>      cpu->cpu_index = -1;
>      cpu_list_unlock();

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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