Re: [Qemu-devel] [PATCH] accel/tcg/cputlb: avoid recursive BQL (fixes #1706296)

[Michael Roth]

Quoting Alex Bennée (2017-09-21 06:06:25)
> The mmio path (see exec.c:prepare_mmio_access) already protects itself
> against recursive locking and it makes sense to do the same for
> io_readx/writex. Otherwise any helper running in the BQL context will
> assert when it attempts to write to device memory as in the case of
> the bug report.
> 
> Signed-off-by: Alex Bennée <address@hidden>
> CC: Richard Jones <address@hidden>
> CC: Paolo Bonzini <address@hidden>

FYI: this patch has been tagged for stable 2.10.1, but is not yet
upstream. Patch freeze for 2.10.1 is September 27th.

> ---
>  accel/tcg/cputlb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
> index e72415a882..bcbcc4db6c 100644
> --- a/accel/tcg/cputlb.c
> +++ b/accel/tcg/cputlb.c
> @@ -765,7 +765,7 @@ static uint64_t io_readx(CPUArchState *env, CPUIOTLBEntry 
> *iotlbentry,
> 
>      cpu->mem_io_vaddr = addr;
> 
> -    if (mr->global_locking) {
> +    if (mr->global_locking && !qemu_mutex_iothread_locked()) {
>          qemu_mutex_lock_iothread();
>          locked = true;
>      }
> @@ -800,7 +800,7 @@ static void io_writex(CPUArchState *env, CPUIOTLBEntry 
> *iotlbentry,
>      cpu->mem_io_vaddr = addr;
>      cpu->mem_io_pc = retaddr;
> 
> -    if (mr->global_locking) {
> +    if (mr->global_locking && !qemu_mutex_iothread_locked()) {
>          qemu_mutex_lock_iothread();
>          locked = true;
>      }
> -- 
> 2.14.1
> 
>