Re: [PATCH v6 1/4] mm/slub: enable debugging memory wasting of kmalloc

[Feng Tang]

On Tue, Nov 01, 2022 at 07:39:13PM +0000, John Thomson wrote:
> 
> 
> On Tue, 1 Nov 2022, at 13:55, Feng Tang wrote:
> > On Tue, Nov 01, 2022 at 06:42:23PM +0800, Hyeonggon Yoo wrote:
> >> setup_arch() is too early to use slab allocators.
> >> I think slab received NULL pointer because kmalloc is not initialized.
> >> 
> >> It seems arch/mips/ralink/mt7621.c is using slab too early.
> >
> > Cool! it is finally root caused :) Thanks!
> >
> > The following patch should solve it and give it a warning message, though
> > I'm not sure if there is other holes.  
> >
> > Thanks,
> > Feng
> >
> > ---
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index 33b1886b06eb..429c21b7ecbc 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -1043,7 +1043,14 @@ size_t __ksize(const void *object)
> >  #ifdef CONFIG_TRACING
> >  void *kmalloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
> >  {
> > -	void *ret = __kmem_cache_alloc_node(s, gfpflags, NUMA_NO_NODE,
> > +	void *ret;
> > +
> > +	if (unlikely(ZERO_OR_NULL_PTR(s))) {
> > +		WARN_ON_ONCE(1);
> > +		return s;
> > +	}
> > +
> > +	ret = __kmem_cache_alloc_node(s, gfpflags, NUMA_NO_NODE,
> >  					    size, _RET_IP_);
> > 
> >  	trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags, NUMA_NO_NODE);
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 157527d7101b..85d24bb6eda7 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -3410,8 +3410,14 @@ static __always_inline
> >  void *__kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
> >  			     gfp_t gfpflags)
> >  {
> > -	void *ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
> > +	void *ret;
> > 
> > +	if (unlikely(ZERO_OR_NULL_PTR(s))) {
> > +		WARN_ON_ONCE(1);
> > +		return s;
> > +	}
> > +
> > +	ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
> >  	trace_kmem_cache_alloc(_RET_IP_, ret, s, gfpflags, NUMA_NO_NODE);
> > 
> >  	return ret;
> 
> Yes, thank you, that patch atop v6.1-rc3 lets me boot, and shows the warning and stack dump.
> Will you submit that, or how do we want to proceed?

Thanks for confirming. I wanted to wait for Vlastimil, Hyeonggon and
other developer's opinion. And yes, I can also post a more formal one.

> transfer started ......................................... transfer ok, time=2.11s
> setting up elf image... OK
> jumping to kernel code
> zimage at:     80B842A0 810B4BC0
> 
> Uncompressing Linux at load address 80001000
> 
> Copy device tree to address  80B80EE0
> 
> Now, booting the kernel...
> 
> [    0.000000] Linux version 6.1.0-rc3+ (john@john) (mipsel-buildroot-linux-gnu-gcc.br_real (Buildroot 2021.11-4428-g6b6741b) 12.2.0, GNU ld (GNU Binutils) 2.39) #73 SMP Wed Nov  2 05:10:01 AEST 2022
> [    0.000000] ------------[ cut here ]------------
> [    0.000000] WARNING: CPU: 0 PID: 0 at mm/slub.c:3416 kmem_cache_alloc+0x5a4/0x5e8
> [    0.000000] Modules linked in:
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 6.1.0-rc3+ #73
> [    0.000000] Stack : 810fff78 80084d98 00000000 00000004 00000000 00000000 80889d04 80c90000
> [    0.000000]         80920000 807bd328 8089d368 80923bd3 00000000 00000001 80889cb0 00000000
> [    0.000000]         00000000 00000000 807bd328 8084bcb1 00000002 00000002 00000001 6d6f4320
> [    0.000000]         00000000 80c97d3d 80c97d68 fffffffc 807bd328 00000000 00000000 00000000
> [    0.000000]         00000000 a0000000 80910000 8110a0b4 00000000 00000020 80010000 80010000
> [    0.000000]         ...
> [    0.000000] Call Trace:
> [    0.000000] [<80008260>] show_stack+0x28/0xf0
> [    0.000000] [<8070c958>] dump_stack_lvl+0x60/0x80
> [    0.000000] [<8002e184>] __warn+0xc4/0xf8
> [    0.000000] [<8002e210>] warn_slowpath_fmt+0x58/0xa4
> [    0.000000] [<801c0fac>] kmem_cache_alloc+0x5a4/0x5e8
> [    0.000000] [<8092856c>] prom_soc_init+0x1fc/0x2b4
> [    0.000000] [<80928060>] prom_init+0x44/0xf0
> [    0.000000] [<80929214>] setup_arch+0x4c/0x6a8
> [    0.000000] [<809257e0>] start_kernel+0x88/0x7c0
> [    0.000000] 
> [    0.000000] ---[ end trace 0000000000000000 ]---
> [    0.000000] SoC Type: MediaTek MT7621 ver:1 eco:3
> [    0.000000] printk: bootconsole [early0] enabled
> 
> Thank you for working through this with me.
> I will try to address the root cause in mt7621.c.
> It looks like other arch/** soc_device_register users use postcore_initcall, device_initcall,
> or the ARM DT_MACHINE_START .init_machine. A quick hack to use postcore_initcall in mt7621
> avoided this zero ptr kmem_cache passed to kmem_cache_alloc_lru.

If IIUC, the prom_soc_init() is only called once in kernel, can the
'soc_dev_attr' just be defined as a global data structure instead
of calling kzalloc(), as its size is small only containing 7 pointers.

Thanks,
Feng