Re: [PATCH v2 2/2] module: Merge same-name module load requests

[Prarit Bhargava]

On 11/14/22 10:45, David Hildenbrand wrote:
> On 14.11.22 16:38, Luis Chamberlain wrote:
> > On Mon, Nov 14, 2022 at 09:57:56AM +0100, David Hildenbrand wrote:
> > > On 12.11.22 02:47, Luis Chamberlain wrote:
> > > > On Wed, Oct 19, 2022 at 02:00:55PM +0200, Petr Pavlu wrote:
> > > > > On 10/18/22 20:33, Luis Chamberlain wrote:
> > > > > > On Sat, Oct 15, 2022 at 11:27:10AM +0200, Petr Pavlu wrote:
> > > > > > > The patch does address a regression observed after commit 
> > > > > > > 6e6de3dee51a
> > > > > > > ("kernel/module.c: Only return -EEXIST for modules that have 
> > > > > > > finished
> > > > > > > loading"). I guess it can have a Fixes tag added to the patch.
> > > > > > >
> > > > > > > I think it is hard to split this patch into parts because the 
> > > > > > > implemented
> > > > > > > "optimization" is the fix.
> > > > > >
> > > > > > git describe --contains 6e6de3dee51a
> > > > > > v5.3-rc1~38^2~6
> > > > > >
> > > > > > I'm a bit torn about this situation. Reverting 6e6de3dee51a would 
> > > > > > be the
> > > > > > right thing to do, but without it, it still leaves the issue reported
> > > > > > by Prarit Bhargava. We need a way to resolve the issue on stable and
> > > > > > then your optimizations can be applied on top.
> > > > >
> > > > > Simpler could be to do the following:
> > > > >
> > > > > diff --git a/kernel/module/main.c b/kernel/module/main.c
> > > > > index d02d39c7174e..0302ac387e93 100644
> > > > > --- a/kernel/module/main.c
> > > > > +++ b/kernel/module/main.c
> > > > > @@ -2386,7 +2386,8 @@ static bool finished_loading(const char *name)
> > > > >        sched_annotate_sleep();
> > > > >        mutex_lock(&module_mutex);
> > > > >        mod = find_module_all(name, strlen(name), true);
> > > > > -    ret = !mod || mod->state == MODULE_STATE_LIVE;
> > > > > +    ret = !mod || mod->state == MODULE_STATE_LIVE
> > > > > +        || mod->state == MODULE_STATE_GOING;
> > > > >        mutex_unlock(&module_mutex);
> > > > >        return ret;
> > > > > @@ -2566,7 +2567,8 @@ static int add_unformed_module(struct module 
> > > > > *mod)
> > > > >        mutex_lock(&module_mutex);
> > > > >        old = find_module_all(mod->name, strlen(mod->name), true);
> > > > >        if (old != NULL) {
> > > > > -        if (old->state != MODULE_STATE_LIVE) {
> > > > > +        if (old->state == MODULE_STATE_COMING
> > > > > +            || old->state == MODULE_STATE_UNFORMED) {
> > > > >                /* Wait in case it fails to load. */
> > > > >                mutex_unlock(&module_mutex);
> > > > >                err = wait_event_interruptible(module_wq,
> > > > > @@ -2575,7 +2577,7 @@ static int add_unformed_module(struct module 
> > > > > *mod)
> > > > >                    goto out_unlocked;
> > > > >                goto again;
> > > > >            }
> > > > > -        err = -EEXIST;
> > > > > +        err = old->state != MODULE_STATE_LIVE ? -EBUSY : -EEXIST;
> > > > >            goto out;
> > > > >        }
> > > > >        mod_update_bounds(mod);
> > > >
> > > >
> > > > Prarit, can you verify this still does not break the issue you 
> > > > reported?
> > > > David, does this also fix your issue?
> > >
> > > I didn't try, but from a quick glimpse I assume no. Allocating module 
> > > space
> > > happens before handling eventual duplicates right now, before a 
> > > module even
> > > is "alive" and in the MODULE_STATE_UNFORMED state.
> >
> > The first two hunks are a revert of commit 6e6de3dee51a and I'm under
> > the impression that cauased your issues as *more* modules states are
> > allowed through.
> >
> > The last hunk tries to fix what 6e6de3dee51a wanted to do.
>
> Note that I don't think the issue I raised is due to 6e6de3dee51a.
>
> > > But maybe I am missing something important.
> >
> > Please do test if you can.
>
> I don't have the machine at hand right now. But, again, I doubt this 
> will fix it.
>
>
> The flow is in load_module():
>
>      mod = layout_and_allocate(info, flags);
>      if (IS_ERR(mod)) {
>          ...
>      }
>
>      audit_log_kern_module(mod->name);
>
>      /* Reserve our place in the list. */
>      err = add_unformed_module(mod);
>      if (err)
>          goto free_module;
>
>
> You can have 400 threads in layout_and_allocate() loading the same 
> module at the same time and running out of module space. Any changes to 
> add_unformed_module() and finished_loading() won't change that, because 
> they are not involved before the module space allocations happened.

I'd like to see a refreshed patch but I tested the latest version and 
see that the boot time is LONGER with the change

Before:

[11:17 AM root@intel-eaglestream-spr-15 kernel-ark]# systemd-analyze
Startup finished in 55.418s (firmware) + 22.766s (loader) + 35.856s 
(kernel) + 5.830s (initrd) + 15.671s (userspace) = 2min 15.542s
multi-user.target reached after 15.606s in userspace.

After:

Startup finished in 55.314s (firmware) + 23.033s (loader) + 35.331s 
(kernel) + 5.176s (initrd) + 23.465s (userspace) = 2min 22.320s
multi-user.target reached after 23.093s in userspace.

Subsequent reboots also indicate that userspace boot time is longer 
after the change.

P.