Re: [PATCH v2 3/5] memfd: improve userspace warnings for missing exec-related flags

[Aleksa Sarai]

On 2023-09-02, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 1 Sep 2023 07:13:45 +0200 Damian Tometzki <dtometzki@xxxxxxxxxxxxxxxxx> wrote:
> 
> > >  	if (!(flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
> > > -		pr_warn_once(
> > > +		pr_info_ratelimited(
> > >  			"%s[%d]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set\n",
> > >  			current->comm, task_pid_nr(current));
> > >  	}
> > > 
> > > -- 
> > > 2.41.0
> > >
> > Hello Sarai,
> > 
> > i got a lot of messages in dmesg with this. DMESG is unuseable with
> > this. 
> > [ 1390.349462] __do_sys_memfd_create: 5 callbacks suppressed
> > [ 1390.349468] pipewire-pulse[2930]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
> > [ 1390.350106] pipewire[2712]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
> 
> OK, thanks, I'll revert this.  Spamming everyone even harder isn't a
> good way to get developers to fix their stuff.

Sorry, I'm on vacation. I will send a follow-up patch to remove this
logging entirely -- if we can't do rate-limited logging then logging a
single message effectively at boot time makes no sense. I had hoped that
this wouldn't be too much (given there is a fair amount of INFO-level
spam in the kernel log) but I guess the default ratelimit (5Hz) is too
liberal.

Perhaps we can re-consider adding some logging in the future, when more
programs have migrated. The only other "reasonable" way to reduce the
logging would be to add something to task_struct so we only log once per
task, but obviously that's massively overkill.

(FWIW, I don't think the logging was ever necessary. There's nothing
wrong with running an older program that doesn't pass the flags.)

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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