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Re: [Qemu-devel] [PATCH] cpu-exec: Exit exclusive region on longjmp from
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [PATCH] cpu-exec: Exit exclusive region on longjmp from step_atomic |
Date: |
Thu, 02 Nov 2017 16:00:22 +0000 |
User-agent: |
mu4e 1.0-alpha0; emacs 26.0.90 |
Peter Maydell <address@hidden> writes:
> Commit ac03ee5331612e44be narrowed the scope of the exclusive
> region so it only covers when we're executing the TB, not when
> we're generating it. However it missed that there is more than
> one execution path out of cpu_tb_exec -- if the atomic insn
> causes an exception then the code will longjmp out, skipping
> the code to end the exclusive region. This causes QEMU to hang
> the next time the CPU calls start_exclusive(), waiting for
> itself to exit the region.
>
> Move the "end the region" code out to the end of the
> function so that it is run for both normal exit and also
> for exit-via-longjmp.
>
> (For some reason this only reproduces for me with a clang
> optimized build, not a gcc debug build.)
>
> Fixes: ac03ee5331612e44beb393df2b578c951d27dc0d
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> accel/tcg/cpu-exec.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 4318441..ac316bb 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -256,9 +256,6 @@ void cpu_exec_step_atomic(CPUState *cpu)
> trace_exec_tb(tb, pc);
> cpu_tb_exec(cpu, tb);
> cc->cpu_exec_exit(cpu);
> - parallel_cpus = true;
> -
> - end_exclusive();
> } else {
> /* We may have exited due to another problem here, so we need
> * to reset any tb_locks we may have taken but didn't release.
> @@ -270,6 +267,9 @@ void cpu_exec_step_atomic(CPUState *cpu)
> #endif
> tb_lock_reset();
> }
> +
> + parallel_cpus = true;
> + end_exclusive();
We assume sigsetjmp can never fail - we either set the jump or are
returning from a longjmp back. So we can never be in the position of
having not been through start_exclusive?
What happens for example if we fault during translation?
--
Alex Bennée