[PATCH V3] riscv: errata: Add ERRATA_THEAD_WRITE_ONCE fixup

[Guo Ren]

On Thu, Feb 19, 2026 at 4:05 PM Yao Zi <me at ziyao.cc> wrote:
>
> On Sun, Jan 25, 2026 at 01:39:41AM -0500, guoren at kernel.org wrote:
> > From: "Guo Ren (Alibaba DAMO Academy)" <guoren at kernel.org>
> >
> > The early version of XuanTie C910 core has a store merge buffer
> > delay problem. The store merge buffer could improve the store queue
> > performance by merging multi-store requests, but when there are not
> > continued store requests, the prior single store request would be
> > waiting in the store queue for a long time. That would cause
> > significant problems for communication between multi-cores. This
> > problem was found on sg2042 & th1520 platforms with the qspinlock
> > lock torture test.
> >
> > So appending a fence w.o could immediately flush the store merge
> > buffer and let other cores see the write result.
> >
> > This will apply the WRITE_ONCE errata to handle the non-standard
> > behavior via appending a fence w.o instruction for WRITE_ONCE().
> >
> > This problem is only observed on the sg2042 hardware platform by
> > running the lock_torture test program for half an hour. The problem
> > was not found in the user space application, because interrupt can
> > break the livelock.
> >
> > Reviewed-by: Leonardo Bras <leobras at redhat.com>
> > Tested-by: Han Gao <gaohan at iscas.ac.cn>
> > Cc: Yao Zi <me at ziyao.cc>
> > Cc: Alexandre Ghiti <alexghiti at rivosinc.com>
> > Cc: Paul Walmsley <pjw at kernel.org>
> > Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren at kernel.org>
>
> With the patch, I've run heavy multi-core compilation load on SG2042 for
> more than 12 hours, and observed no stability issues.
>
> Tested-by: Yao Zi <me at ziyao.cc>

Thx for the Tested-by, hope this patch could be adopted.

-- 
Best Regards
 Guo Ren