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Re: [Qemu-devel] [PATCH v2] cpu-exec: Exit exclusive region on longjmp f

From: Emilio G. Cota
Subject: Re: [Qemu-devel] [PATCH v2] cpu-exec: Exit exclusive region on longjmp from step_atomic
Date: Thu, 2 Nov 2017 13:15:38 -0400
User-agent: Mutt/1.5.24 (2015-08-30)

On Thu, Nov 02, 2017 at 16:35:36 +0000, Peter Maydell wrote:
> 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. We have to use a volatile bool flag
> to decide whether we need to end the region, because we
> can longjump out of the codegen as well as the execution.
> (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>

Reviewed-by: Emilio G. Cota <address@hidden>

Good catch, thanks for the fix!


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