linux-kernel - Re: [PATCH 6.6] membarrier: riscv: Add full memory barrier in switch

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Message-ID: <2024091037-errant-countdown-4928@gregkh>
Date: Tue, 10 Sep 2024 13:58:02 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Alexandre Ghiti <alex@...ti.fr>
Cc: WangYuli <wangyuli@...ontech.com>, stable@...r.kernel.org,
	sashal@...nel.org, parri.andrea@...il.com,
	mathieu.desnoyers@...icios.com, palmer@...osinc.com,
	linux-kernel@...r.kernel.org, paul.walmsley@...ive.com,
	palmer@...belt.com, aou@...s.berkeley.edu, nathan@...nel.org,
	ndesaulniers@...gle.com, trix@...hat.com,
	linux-riscv@...ts.infradead.org, llvm@...ts.linux.dev,
	paulmck@...nel.org, mingo@...hat.com, peterz@...radead.org,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
	brauner@...nel.org, arnd@...db.de
Subject: Re: [PATCH 6.6] membarrier: riscv: Add full memory barrier in
 switch_mm()

On Tue, Sep 10, 2024 at 01:31:04PM +0200, Alexandre Ghiti wrote:
> 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@...il.com>
> > > 
> > > [ 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@...il.com>
> > > Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > > Link: https://lore.kernel.org/r/20240131144936.29190-2-parri.andrea@gmail.com
> > > Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
> > > Signed-off-by: WangYuli <wangyuli@...ontech.com>
> > > ---
> > >   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?

Yes, you didn't tag cc: stable at all in this commit, which is why we
did not see it.  The documentation says that :)

thanks,

greg k-h