Re: [PATCH 6.6] membarrier: riscv: Add full memory barrier in switch_mm()

[Alexandre Ghiti]

Hi Greg,

On 10/09/2024 09:32, Greg KH wrote:
> On Mon, Sep 09, 2024 at 10:57:01AM +0800, WangYuli wrote:
> > From: Andrea Parri <parri.andrea@xxxxxxxxx>
> >
> > [ Upstream commit d6cfd1770f20392d7009ae1fdb04733794514fa9 ]
> >
> > The membarrier system call requires a full memory barrier after storing
> > to rq->curr, before going back to user-space.  The barrier is only
> > needed when switching between processes: the barrier is implied by
> > mmdrop() when switching from kernel to userspace, and it's not needed
> > when switching from userspace to kernel.
> >
> > Rely on the feature/mechanism ARCH_HAS_MEMBARRIER_CALLBACKS and on the
> > primitive membarrier_arch_switch_mm(), already adopted by the PowerPC
> > architecture, to insert the required barrier.
> >
> > Fixes: fab957c11efe2f ("RISC-V: Atomic and Locking Code")
> > Signed-off-by: Andrea Parri <parri.andrea@xxxxxxxxx>
> > Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20240131144936.29190-2-parri.andrea@xxxxxxxxx
> > Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
> > Signed-off-by: WangYuli <wangyuli@xxxxxxxxxxxxx>
> > ---
> >   MAINTAINERS                         |  2 +-
> >   arch/riscv/Kconfig                  |  1 +
> >   arch/riscv/include/asm/membarrier.h | 31 +++++++++++++++++++++++++++++
> >   arch/riscv/mm/context.c             |  2 ++
> >   kernel/sched/core.c                 |  5 +++--
> >   5 files changed, 38 insertions(+), 3 deletions(-)
> >   create mode 100644 arch/riscv/include/asm/membarrier.h
> Now queued up, thanks.


The original patch was merged in 6.9 and the Fixes tag points to a 
commit introduced in v4.15. So IIUC, this patch should have been 
backported "automatically" to the releases < 6.9 right? As stated in the 
documentation (process/stable-kernel-rules.html):

"Note, such tagging is unnecessary if the stable team can derive the 
appropriate versions from Fixes: tags."

Or did we miss something?

Thanks,

Alex


> greg k-h
>
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