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

[Feng Tang <feng.tang@intel.com>]

On Tue, Nov 01, 2022 at 06:42:23PM +0800, Hyeonggon Yoo wrote:
> On Tue, Nov 01, 2022 at 10:33:32AM +0000, John Thomson wrote:
> > On Tue, 1 Nov 2022, at 09:31, Hyeonggon Yoo wrote:
> > > On Tue, Nov 01, 2022 at 09:20:21AM +0000, John Thomson wrote:
> > >> On Tue, 1 Nov 2022, at 07:57, Feng Tang wrote:
> > >> > Hi Thomson,
> > >> >
> > >> > Thanks for testing!
> > >> >
> > >> > + mips maintainer and mail list. The original report is here
> > >> >
> > >> > https://lore.kernel.org/lkml/becf2ac3-2a90-4f3a-96d9-a70f67c66e4a@app.fastmail.com/
> > >>
> > >> I am guessing my issue comes from __kmem_cache_alloc_lru accessing s->object_size when (kmem_cache) s is NULL?
> > >> If that is the case, this change is not to blame, it only exposes the issue?
> > >> 
> > >> I get the following dmesg (note very early NULL kmem_cache) with the below change atop v6.1-rc3:
> > >> 
> > >> transfer started ......................................... transfer ok, time=2.02s
> > >> setting up elf image... OK
> > >> jumping to kernel code
> > >> zimage at:     80B842A0 810B4EFC
> > >> 
> > >> 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) #61 SMP Tue Nov  1 18:04:13 AEST 2022
> > >> [    0.000000] slub: kmem_cache_alloc called with kmem_cache: 0x0
> > >> [    0.000000] slub: __kmem_cache_alloc_lru called with kmem_cache: 0x0
> > >> [    0.000000] SoC Type: MediaTek MT7621 ver:1 eco:3
> > >> [    0.000000] printk: bootconsole [early0] enabled
> > >> [    0.000000] CPU0 revision is: 0001992f (MIPS 1004Kc)
> > >> [    0.000000] MIPS: machine is MikroTik RouterBOARD 760iGS
> > >> 
> > >> normal boot
> > >> 
> > >> 
> > >> diff --git a/mm/slub.c b/mm/slub.c
> > >> index 157527d7101b..10fcdf2520d2 100644
> > >> --- a/mm/slub.c
> > >> +++ b/mm/slub.c
> > >> @@ -3410,7 +3410,13 @@ 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 (IS_ERR_OR_NULL(s)) {
> > >> +		pr_warn("slub: __kmem_cache_alloc_lru called with kmem_cache: %pSR\n", s);
> > >> +		ret = slab_alloc(s, lru, gfpflags, _RET_IP_, 0);
> > >> +	} else {
> > >> +		ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
> > >> +	}
> > >>  
> > >>  	trace_kmem_cache_alloc(_RET_IP_, ret, s, gfpflags, NUMA_NO_NODE);
> > >>  
> > >> @@ -3419,6 +3425,8 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
> > >>  
> > >>  void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
> > >>  {
> > >> +	if (IS_ERR_OR_NULL(s))
> > >> +		pr_warn("slub: kmem_cache_alloc called with kmem_cache: %pSR\n", s);
> > >>  	return __kmem_cache_alloc_lru(s, NULL, gfpflags);
> > >>  }
> > >>  EXPORT_SYMBOL(kmem_cache_alloc);
> > >> @@ -3426,6 +3434,8 @@ EXPORT_SYMBOL(kmem_cache_alloc);
> > >>  void *kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
> > >>  			   gfp_t gfpflags)
> > >>  {
> > >> +	if (IS_ERR_OR_NULL(s))
> > >> +		pr_warn("slub: __kmem_cache_alloc_lru called with kmem_cache: %pSR\n", s);
> > >>  	return __kmem_cache_alloc_lru(s, lru, gfpflags);
> > >>  }
> > >>  EXPORT_SYMBOL(kmem_cache_alloc_lru);
> > >> 
> > >> 
> > >> Any hints on where kmem_cache_alloc would be being called from this early?
> > >> I will start looking from /init/main.c around pr_notice("%s", linux_banner);
> > >
> > > Great. Would you try calling dump_stack(); when we observed s == NULL?
> > > That would give more information about who passed s == NULL to these
> > > functions.
> > >
> > 
> > With the dump_stack() in place:
> > 
> > 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) #62 SMP Tue Nov  1 19:49:52 AEST 2022
> > [    0.000000] slub: __kmem_cache_alloc_lru called with kmem_cache ptr: 0x0
> > [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 6.1.0-rc3+ #62
> > [    0.000000] Stack : 810fff78 80084d98 80889d00 00000004 00000000 00000000 80889d5c 80c90000
> > [    0.000000]         80920000 807bd380 8089d368 80923bd3 00000000 00000001 80889d08 00000000
> > [    0.000000]         00000000 00000000 807bd380 8084bd51 00000002 00000002 00000001 6d6f4320
> > [    0.000000]         00000000 80c97ce9 80c97d14 fffffffc 807bd380 00000000 00000003 00000dc0
> > [    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] [<8070cdc0>] dump_stack_lvl+0x60/0x80
> > [    0.000000] [<801c1428>] kmem_cache_alloc+0x5c0/0x740
> > [    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] SoC Type: MediaTek MT7621 ver:1 eco:3
> 
> 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;