Re: [PATCH] HWPOISON: add a pr_err message when forcibly send a sigbus

[Helge Deller]

On 8/31/23 05:29, Shuai Xue wrote:
> On 2023/8/31 06:18, Will Deacon wrote:
> > On Mon, Aug 28, 2023 at 09:41:55AM +0800, Shuai Xue wrote:
> > > On 2023/8/22 09:15, Shuai Xue wrote:
> > > > On 2023/8/21 18:50, Will Deacon wrote:
> > > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > > > index 3fe516b32577..38e2186882bd 100644
> > > > > > --- a/arch/arm64/mm/fault.c
> > > > > > +++ b/arch/arm64/mm/fault.c
> > > > > > @@ -679,6 +679,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
> > > > > >   	} else if (fault & (VM_FAULT_HWPOISON_LARGE | VM_FAULT_HWPOISON)) {
> > > > > >   		unsigned int lsb;
> > > > > >
> > > > > > +		pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
> > > > > > +		       current->comm, current->pid, far);
> > > > > >   		lsb = PAGE_SHIFT;
> > > > > >   		if (fault & VM_FAULT_HWPOISON_LARGE)
> > > > > >   			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
> > > > >
> > > > > Hmm, I'm not convinced by this. We have 'show_unhandled_signals' already,
> > > > > and there's plenty of code in memory-failure.c for handling poisoned pages
> > > > > reported by e.g. GHES. I don't think dumping extra messages in dmesg from
> > > > > the arch code really adds anything.
> > > >
> > > > I see the show_unhandled_signals() will dump the stack but it rely on
> > > > /proc/sys/debug/exception-trace be set.
> > > >
> > > > The memory failure is the top issue in our production cloud and also other hyperscalers.
> > > > We have received complaints from our operations engineers and end users that processes
> > > > are being inexplicably killed :(. Could you please consider add a message?
> >
> > I don't have any objection to logging this stuff somehow, I'm just not
> > convinced that the console is the best place for that information in 2023.
> > Is there really nothing better?

> I agree that console might not the better place, but it still plays an important role.
> IMO the most direct idea for end user to check what happened is to check by viewing
> the dmesg. In addition, we deployed some log store service collects all cluster dmesg
> from /var/log/kern.

Right, pr_err() is not just console.
It ends up in the syslog, which ends up in a lot of places, e.g. through syslog forwarding.
Most monitoring tools monitor the syslog as well.

So, IMHO pr_err() is the right thing.

Helge



> Hi, Will,



> Do you have any better choice?
>
> + @Tony for ERST
> I found that after /dev/mcelog driver deprecated, both x86 and ARM64 platform does not
> support to collect MCE record of previous boot in persistent storage via APEI ERST.
> I propose to add a mechanism to do it for rasdaemon. Do you have any suggestion?
>
> Thank you.
> Best Regards,
> Shuai