Re: [PATCH v2] mm/slub: Add check for s->flags in the alloc_tagging_slab_free_hook

[Vlastimil Babka <vbabka@suse.cz>]

On 8/16/24 03:33, Hao Ge wrote:
> From: Hao Ge <gehao@kylinos.cn>
> 
> 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,
> because it has already been assigned a value in kfence_init_pool.
> 
> 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.
> 
> 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@kylinos.cn>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/slub.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index c9d8a2497fd6..a77f354f8325 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2116,6 +2116,10 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
>  	if (!mem_alloc_profiling_enabled())
>  		return;
>  
> +	/* slab->obj_exts might not be NULL if it was created for MEMCG accounting. */
> +	if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
> +		return;
> +
>  	obj_exts = slab_obj_exts(slab);
>  	if (!obj_exts)
>  		return;