On 11/1/22 11:33, 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@xxxxxxxxxxxxxxxx/ >>> >>> 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 The stack means CONFIG_TRACING=n, is that right? That would mean prom_soc_init() soc_dev_init() kzalloc() -> kmalloc() kmalloc_trace() // after #else /* CONFIG_TRACING */ kmem_cache_alloc(s, flags); Looks like this path is a small bug in the wasting detection patch, as we throw away size there. AFAICS before this patch, we "survive" "kmem_cache *s" being NULL as slab_pre_alloc_hook() will happen to return NULL and we bail out from slab_alloc_node(). But this is a side-effect, not an intended protection. Also the CONFIG_TRACING variant of kmalloc_trace() would have called trace_kmalloc dereferencing s->size anyway even before this patch. I don't think we should add WARNS in the slab hot paths just to prevent this rare error of using slab too early. At most VM_WARN... would be acceptable but still not necessary as crashing immediately from a NULL pointer is sufficient. So IMHO mips should fix their soc init, and we should look into the CONFIG_TRACING=n variant of kmalloc_trace(), to pass orig_size properly.
