Re: [PATCH v2] x86/mce: Fix endless loop when run task works after #MC

On Tue, Jul 06, 2021 at 08:16:06PM +0800, Ding Hui wrote:

Recently we encounter multi #MC on the same task when it's task_work_run() has not been called, current->mce_kill_me was added to task_works list more than once, that make a circular linked task_works, so task_work_run() will do a endless loop.

I saw the same and posted a similar fix a while back:

https://www.spinics.net/lists/linux-mm/msg251006.html

It didn't get merged because some validation tests began failing around the same time. I'm now pretty sure I understand what happened with those other tests.

I'll post my updated version (second patch in a three part series) later today.

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c

• if (!cmpxchg(&current->mce_kill_me.func, NULL, ch.func)) {

• current->mce_addr = m->addr;
  

• current->mce_kflags = m->kflags;
  

• current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV);
  

• current->mce_whole_page = whole_page(m);
  

You don't need an atomic cmpxchg here (nor the WRITE_ONCE() to clear it). The task is operating on its own task_struct. Nobody else should touch the mce_kill_me field.

-Tony