Re: [PATCH v1 1/5] mm/memory_hotplug: check for fatal signals only in offline_pages()

[David Hildenbrand]

On 27.06.23 14:34, Michal Hocko wrote:
> On Tue 27-06-23 13:22:16, David Hildenbrand wrote:
> > Let's check for fatal signals only. That looks cleaner and still keeps
> > the documented use case for manual user-space triggered memory offlining
> > working. From Documentation/admin-guide/mm/memory-hotplug.rst:
> >
> > 	% timeout $TIMEOUT offline_block | failure_handling
> >
> > In fact, we even document there: "the offlining context can be terminated
> > by sending a fatal signal".
>
> We should be fixing documentation instead. This could break users who do
> have a SIGALRM signal hander installed.

You mean because timeout will send a SIGALRM, which is not considered 
fatal in case a signal handler is installed?

At least the "traditional" tools I am aware of don't set a timeout at 
all (crossing fingers that they never end up stuck):
* chmem
* QEMU guest agent
* powerpc-utils

libdaxctl also doesn't seem to implement an easy-to-spot timeout for 
memory offlining, but it also doesn't configure SIGALRM.


Of course, that doesn't mean that there isn't somewhere a program that 
does that; I merely assume that it would be pretty unlikely to find such 
a program.

But no strong opinion: we can also keep it like that, update the doc and 
add a comment why this one here is different than most other signal 
backoff checks.


Thanks!

--
Cheers,

David / dhildenb