Re: slub: don't panic for memcg kmem cache creation failure
On Sat, Jun 29, 2019 at 7:05 AM Alexey Dobriyan 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
Re: slub: don't panic for memcg kmem cache creation failure
> - 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.
Re: [PATCH] slub: Don't panic for memcg kmem cache creation failure
On Wed, 19 Jun 2019, Shakeel Butt wrote: > Currently for CONFIG_SLUB, if a memcg kmem cache creation is failed and > the corresponding root kmem cache has SLAB_PANIC flag, the kernel will > be crashed. This is unnecessary as the kernel can handle the creation > failures of memcg kmem caches. Additionally CONFIG_SLAB does not > implement this behavior. So, to keep the behavior consistent between > SLAB and SLUB, removing the panic for memcg kmem cache creation > failures. The root kmem cache creation failure for SLAB_PANIC correctly > panics for both SLAB and SLUB. > > Reported-by: Dave Hansen > Signed-off-by: Shakeel Butt Acked-by: David Rientjes
Re: [PATCH] slub: Don't panic for memcg kmem cache creation failure
On Thu 20-06-19 07:44:27, Shakeel Butt wrote: > On Wed, Jun 19, 2019 at 10:50 PM Michal Hocko wrote: > > > > On Wed 19-06-19 16:25:14, Shakeel Butt wrote: > > > Currently for CONFIG_SLUB, if a memcg kmem cache creation is failed and > > > the corresponding root kmem cache has SLAB_PANIC flag, the kernel will > > > be crashed. This is unnecessary as the kernel can handle the creation > > > failures of memcg kmem caches. > > > > AFAICS it will handle those by simply not accounting those objects > > right? > > > > The memcg kmem cache creation is async. The allocation has already > been decided not to be accounted on creation trigger. If memcg kmem > cache creation is failed, it will fail silently and the next > allocation will trigger the creation process again. Ohh, right I forgot that it will get retried. This would be useful to mention in the changelog as it is not straightforward from reading just the particular function. > > > Additionally CONFIG_SLAB does not > > > implement this behavior. So, to keep the behavior consistent between > > > SLAB and SLUB, removing the panic for memcg kmem cache creation > > > failures. The root kmem cache creation failure for SLAB_PANIC correctly > > > panics for both SLAB and SLUB. > > > > I do agree that panicing is really dubious especially because it opens > > doors to shut the system down from a restricted environment. So the > > patch makes sesne to me. > > > > I am wondering whether SLAB_PANIC makes sense in general though. Why is > > it any different from any other essential early allocations? We tend to > > not care about allocation failures for those on bases that the system > > must be in a broken state to fail that early already. Do you think it is > > time to remove SLAB_PANIC altogether? > > > > That would need some investigation into the history of SLAB_PANIC. I > will look into it. Well, I strongly suspect this is a relict from the past. I have hard time to believe that the system would get to a usable state if many of those caches would fail to allocate. And as Dave said in his reply it is quite silly to give this weapon to a random driver hands. Everybody just thinks his toy is the most important one... -- Michal Hocko SUSE Labs
Re: [PATCH] slub: Don't panic for memcg kmem cache creation failure
On 6/20/19 7:44 AM, Shakeel Butt wrote:
>> I am wondering whether SLAB_PANIC makes sense in general though. Why is
>> it any different from any other essential early allocations? We tend to
>> not care about allocation failures for those on bases that the system
>> must be in a broken state to fail that early already. Do you think it is
>> time to remove SLAB_PANIC altogether?
>>
> That would need some investigation into the history of SLAB_PANIC. I
> will look into it.
I think it still makes sense for things like the vma, filp, dentry
caches. If we don't
have those, we can't even execve("/sbin/init") so we shouldn't even bother
continuing to boot.
Maybe we should turn off SLAB_PANIC behavior after boot. We don't want
a silly driver or filesystem module that's creating slabs to be causing
panic()s.
Re: [PATCH] slub: Don't panic for memcg kmem cache creation failure
On Wed, Jun 19, 2019 at 10:50 PM Michal Hocko wrote: > > On Wed 19-06-19 16:25:14, Shakeel Butt wrote: > > Currently for CONFIG_SLUB, if a memcg kmem cache creation is failed and > > the corresponding root kmem cache has SLAB_PANIC flag, the kernel will > > be crashed. This is unnecessary as the kernel can handle the creation > > failures of memcg kmem caches. > > AFAICS it will handle those by simply not accounting those objects > right? > The memcg kmem cache creation is async. The allocation has already been decided not to be accounted on creation trigger. If memcg kmem cache creation is failed, it will fail silently and the next allocation will trigger the creation process again. > > Additionally CONFIG_SLAB does not > > implement this behavior. So, to keep the behavior consistent between > > SLAB and SLUB, removing the panic for memcg kmem cache creation > > failures. The root kmem cache creation failure for SLAB_PANIC correctly > > panics for both SLAB and SLUB. > > I do agree that panicing is really dubious especially because it opens > doors to shut the system down from a restricted environment. So the > patch makes sesne to me. > > I am wondering whether SLAB_PANIC makes sense in general though. Why is > it any different from any other essential early allocations? We tend to > not care about allocation failures for those on bases that the system > must be in a broken state to fail that early already. Do you think it is > time to remove SLAB_PANIC altogether? > That would need some investigation into the history of SLAB_PANIC. I will look into it. > > Reported-by: Dave Hansen > > Signed-off-by: Shakeel Butt > > Acked-by: Michal Hocko Thanks.
Re: [PATCH] slub: Don't panic for memcg kmem cache creation failure
On Wed 19-06-19 16:25:14, Shakeel Butt wrote:
> Currently for CONFIG_SLUB, if a memcg kmem cache creation is failed and
> the corresponding root kmem cache has SLAB_PANIC flag, the kernel will
> be crashed. This is unnecessary as the kernel can handle the creation
> failures of memcg kmem caches.
AFAICS it will handle those by simply not accounting those objects
right?
> Additionally CONFIG_SLAB does not
> implement this behavior. So, to keep the behavior consistent between
> SLAB and SLUB, removing the panic for memcg kmem cache creation
> failures. The root kmem cache creation failure for SLAB_PANIC correctly
> panics for both SLAB and SLUB.
I do agree that panicing is really dubious especially because it opens
doors to shut the system down from a restricted environment. So the
patch makes sesne to me.
I am wondering whether SLAB_PANIC makes sense in general though. Why is
it any different from any other essential early allocations? We tend to
not care about allocation failures for those on bases that the system
must be in a broken state to fail that early already. Do you think it is
time to remove SLAB_PANIC altogether?
> Reported-by: Dave Hansen
> Signed-off-by: Shakeel Butt
Acked-by: Michal Hocko
> ---
> mm/slub.c | 4
> 1 file changed, 4 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 6a5174b51cd6..84c6508e360d 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3640,10 +3640,6 @@ static int kmem_cache_open(struct kmem_cache *s,
> slab_flags_t flags)
>
> free_kmem_cache_nodes(s);
> error:
> - 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);
> return -EINVAL;
> }
>
> --
> 2.22.0.410.gd8fdbe21b5-goog
--
Michal Hocko
SUSE Labs
[PATCH] slub: Don't panic for memcg kmem cache creation failure
Currently for CONFIG_SLUB, if a memcg kmem cache creation is failed and
the corresponding root kmem cache has SLAB_PANIC flag, the kernel will
be crashed. This is unnecessary as the kernel can handle the creation
failures of memcg kmem caches. Additionally CONFIG_SLAB does not
implement this behavior. So, to keep the behavior consistent between
SLAB and SLUB, removing the panic for memcg kmem cache creation
failures. The root kmem cache creation failure for SLAB_PANIC correctly
panics for both SLAB and SLUB.
Reported-by: Dave Hansen
Signed-off-by: Shakeel Butt
---
mm/slub.c | 4
1 file changed, 4 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 6a5174b51cd6..84c6508e360d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3640,10 +3640,6 @@ static int kmem_cache_open(struct kmem_cache *s,
slab_flags_t flags)
free_kmem_cache_nodes(s);
error:
- 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);
return -EINVAL;
}
--
2.22.0.410.gd8fdbe21b5-goog
