Am 26.09.2014 13:49, schrieb anton.iva...@kot-begemot.co.uk:
> From: Anton Ivanov <antiv...@cisco.com>
>
> This is a fix for a very old UML bug which can be triggered with stock
> UML. It takes a lot of effort to trigger it there because the
> lseek()/read() | write() mechanics of the UBD driver implicitly sync the
> memory all the time by hitting the appropriate barrier implementation in
> the host kernel.
>
> By improving the disk susbsystem we make this bug raise its ugly head
> with a vengeance - you can get a process in D (with an occasional child
> in Z state) simply by running an apt-get on 30-40 large packages.
>
> Is this correct place to have the sync - no idea. It may need to move
> to somewhere inside tlb.c. With the fence in exec.c it works (TM).
>
> If I understand this correctly, this also needs to be an instruction
> appropriate for the underlying host so just a barrier() will not cut
> it. You have to fence. En-guarde... Touche... :)
>
> Signed-off-by: Anton Ivanov <antiv...@cisco.com>
> ---
> arch/um/kernel/exec.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
> index 0d7103c..7cb6805 100644
> --- a/arch/um/kernel/exec.c
> +++ b/arch/um/kernel/exec.c
> @@ -27,6 +27,11 @@ void flush_thread(void)
> ret = unmap(¤t->mm->context.id, 0, STUB_START, 0, &data);
> ret = ret || unmap(¤t->mm->context.id, STUB_END,
> host_task_size - STUB_END, 1, &data);
> +#ifdef CONFIG_X86_32
> + alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2);
> +#else
> + asm volatile("mfence":::"memory");
> +#endif
Why not mb()?
I'm not sure whether this fix is correct.
Thanks,
//richard
------------------------------------------------------------------------------
Meet PCI DSS 3.0 Compliance Requirements with EventLog Analyzer
Achieve PCI DSS 3.0 Compliant Status with Out-of-the-box PCI DSS Reports
Are you Audit-Ready for PCI DSS 3.0 Compliance? Download White paper
Comply to PCI DSS 3.0 Requirement 10 and 11.5 with EventLog Analyzer
http://pubads.g.doubleclick.net/gampad/clk?id=154622311&iu=/4140/ostg.clktrk
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
