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    SubjectRe: [PATCH] x86/arch_prctl/64: restore accidentally removed put_cpu in ARCH_SET_GS

    * Andy Lutomirski <luto@kernel.org> wrote:

    > On Tue, May 10, 2016 at 1:56 PM, Mateusz Guzik <mguzik@redhat.com> wrote:
    > > This fixes 731e33e39a5b95ad770 "Remove FSBASE/GSBASE < 4G optimization"
    > >
    > > Signed-off-by: Mateusz Guzik <mguzik@redhat.com>
    > > ---
    > > arch/x86/kernel/process_64.c | 1 +
    > > 1 file changed, 1 insertion(+)
    > >
    > > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
    > > index 4285f6a..6b16c36 100644
    > > --- a/arch/x86/kernel/process_64.c
    > > +++ b/arch/x86/kernel/process_64.c
    > > @@ -541,6 +541,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
    > > load_gs_index(0);
    > > ret = wrmsrl_safe(MSR_KERNEL_GS_BASE, addr);
    > > }
    > > + put_cpu();
    > > break;
    > > case ARCH_SET_FS:
    > > /* Not strictly needed for fs, but do it for symmetry
    > > --
    > > 1.8.3.1
    > >
    >
    > Ingo, can you apply this before the merge window opens?

    Yeah, done, applied it to tip:x86/asm.

    > I just noticed that you weren't cc'd, so I'll repeat my ack:
    >
    > Acked-by: Andy Lutomirski <luto@kernel.org>
    >
    > And I'll ask, since IIRC you wrote it: would it make sense to augment
    > lockdep_sys_exit to see if preemption got left disabled?

    Yeah, absolutely. I'm quite sure early lockdep versions did such a check.

    Thanks,

    Ingo

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