On Thu, Aug 15, 2024 at 12:21 AM Hao Ge <hao.ge@xxxxxxxxx> wrote: > > From: Hao Ge <gehao@xxxxxxxxxx> > > When enable CONFIG_MEMCG & CONFIG_KFENCE & CONFIG_KMEMLEAK, > the following warning always occurs,This is because the > following call stack occurred: > mem_pool_alloc > kmem_cache_alloc_noprof > slab_alloc_node > kfence_alloc > > Once the kfence allocation is successful,slab->obj_exts will not be empty. > Since in the prepare_slab_obj_exts_hook function,we perform a check for > s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE),the alloc_tag_add function > will not be called as a result.Therefore,ref->ct remains NULL. > > However,when we call mem_pool_free,since obj_ext is not empty, > it eventually leads to the alloc_tag_sub scenario being invoked. > This is where the warning occurs. Ok, I was trying to understand why "Once the kfence allocation is successful,slab->obj_exts will not be empty.". alloc_slab_obj_exts() has to be called to create slab->obj_exts. Normally that is done in prepare_slab_obj_exts_hook() which has the s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE) check and the cache that kfence_alloc() uses here is the object_cache (passed from mem_pool_alloc()) which has SLAB_NOLEAKTRACE: https://elixir.bootlin.com/linux/v6.11-rc3/source/mm/kmemleak.c#L453. Therefore, prepare_slab_obj_exts_hook() should have skipped it and did not create the slab->obj_exts. So, it must have been called from account_slab() or __memcg_slab_post_alloc_hook() to create slab->obj_exts for memcg accounting in slab->obj_exts.objcg. Ok, now I understand why you need the CONFIG_MEMCG & CONFIG_KFENCE & CONFIG_KMEMLEAK combination. Please confirm that slab->obj_exts creation is happening the way I described above and for those reasons and if so, please update the description of this patch to explain that. > > So we should add corresponding checks in the alloc_tagging_slab_free_hook. > For __GFP_NO_OBJ_EXT case,I didn't see the specific case where it's > using kfence,so I won't add the corresponding check in > alloc_tagging_slab_free_hook for now. > > [ 3.734349] ------------[ cut here ]------------ > [ 3.734807] alloc_tag was not set > [ 3.735129] WARNING: CPU: 4 PID: 40 at ./include/linux/alloc_tag.h:130 kmem_cache_free+0x444/0x574 > [ 3.735866] Modules linked in: autofs4 > [ 3.736211] CPU: 4 UID: 0 PID: 40 Comm: ksoftirqd/4 Tainted: G W 6.11.0-rc3-dirty #1 > [ 3.736969] Tainted: [W]=WARN > [ 3.737258] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022 > [ 3.737875] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > [ 3.738501] pc : kmem_cache_free+0x444/0x574 > [ 3.738951] lr : kmem_cache_free+0x444/0x574 > [ 3.739361] sp : ffff80008357bb60 > [ 3.739693] x29: ffff80008357bb70 x28: 0000000000000000 x27: 0000000000000000 > [ 3.740338] x26: ffff80008207f000 x25: ffff000b2eb2fd60 x24: ffff0000c0005700 > [ 3.740982] x23: ffff8000804229e4 x22: ffff800082080000 x21: ffff800081756000 > [ 3.741630] x20: fffffd7ff8253360 x19: 00000000000000a8 x18: ffffffffffffffff > [ 3.742274] x17: ffff800ab327f000 x16: ffff800083398000 x15: ffff800081756df0 > [ 3.742919] x14: 0000000000000000 x13: 205d344320202020 x12: 5b5d373038343337 > [ 3.743560] x11: ffff80008357b650 x10: 000000000000005d x9 : 00000000ffffffd0 > [ 3.744231] x8 : 7f7f7f7f7f7f7f7f x7 : ffff80008237bad0 x6 : c0000000ffff7fff > [ 3.744907] x5 : ffff80008237ba78 x4 : ffff8000820bbad0 x3 : 0000000000000001 > [ 3.745580] x2 : 68d66547c09f7800 x1 : 68d66547c09f7800 x0 : 0000000000000000 > [ 3.746255] Call trace: > [ 3.746530] kmem_cache_free+0x444/0x574 > [ 3.746931] mem_pool_free+0x44/0xf4 > [ 3.747306] free_object_rcu+0xc8/0xdc > [ 3.747693] rcu_do_batch+0x234/0x8a4 > [ 3.748075] rcu_core+0x230/0x3e4 > [ 3.748424] rcu_core_si+0x14/0x1c > [ 3.748780] handle_softirqs+0x134/0x378 > [ 3.749189] run_ksoftirqd+0x70/0x9c > [ 3.749560] smpboot_thread_fn+0x148/0x22c > [ 3.749978] kthread+0x10c/0x118 > [ 3.750323] ret_from_fork+0x10/0x20 > [ 3.750696] ---[ end trace 0000000000000000 ]--- > > Fixes: 4b8736964640 ("mm/slab: add allocation accounting into slab allocation and free paths") > Signed-off-by: Hao Ge <gehao@xxxxxxxxxx> > --- > mm/slub.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/slub.c b/mm/slub.c > index c9d8a2497fd6..1f67621ba6dc 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2116,6 +2116,9 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p, > if (!mem_alloc_profiling_enabled()) > return; > > + if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE)) > + return; > + Please add a comment before this check saying something like: /* slab->obj_exts might not be NULL if it was created for MEMCG accounting. */ Other than that the fix seems fine to me. Thanks, Suren. > obj_exts = slab_obj_exts(slab); > if (!obj_exts) > return; > -- > 2.25.1 >
