linux-kernel - Re: slub: don't panic for memcg kmem cache creation failure

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Message-ID: <CALvZod4PTevdBfEeea6picRvCfo0m5djcigDF3kd21YULKW31g@mail.gmail.com>
Date:   Sat, 29 Jun 2019 13:31:01 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: slub: don't panic for memcg kmem cache creation failure

On Sat, Jun 29, 2019 at 7:05 AM Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> > -       if (flags & SLAB_PANIC)
> > -               panic("Cannot create slab %s size=%u realsize=%u order=%u offset=%u flags=%lx\n",
> > -                     s->name, s->size, s->size,
> > -                     oo_order(s->oo), s->offset, (unsigned long)flags);
>
> This is wrong. Without SLAB_PANIC people will start to implement error
> checking out of habit and add all slightly different error messages.
> This simply increases text and rodata size.
>
> If memcg kmem caches creation failure is OK, then SLAB_PANIC should not
> be passed.
>
> The fact that SLAB doesn't implement SLAB_PANIC is SLAB bug.

I do not agree with you. IMHO the kmem_cache_create_usercopy() is the
right place to handle SLAB_PANIC which is handling it. If you want
extra info here, you can add pr_warn for SLAB_PANIC here and the
caller will still and rightfully do the panic().

thanks,
Shakeel