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@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 > > 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;
