Re: [PATCH] kfence: free instead of ignore pool from kmemleak

[Marco Elver]

Per Catalin's comment in
https://lore.kernel.org/all/Yvu4bBmykYr+0CXk@xxxxxxx/T/#u
this patch should be ignored, because 6.0-rc1 is fine. We just have to
fix 5.19 by reverting 07313a2b29ed from it.


On Tue, 16 Aug 2022 at 16:25, Marco Elver <elver@xxxxxxxxxx> wrote:
>
> Due to recent changes to kmemleak and how memblock allocated memory is
> stored in the phys object tree of kmemleak, 07313a2b29ed ("mm: kfence:
> apply kmemleak_ignore_phys on early allocated pool") tried to fix KFENCE
> compatibility.
>
> KFENCE's memory can't simply be ignored, but must be freed completely
> due to it being handed out on slab allocations, and the slab post-alloc
> hook attempting to insert the object to the kmemleak object tree.
>
> Without this fix, reports like the below will appear during boot, and
> kmemleak is effectively rendered useless when KFENCE is enabled:
>
>  | kmemleak: Cannot insert 0xffffff806e24f000 into the object search tree (overlaps existing)
>  | CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-v8-0815+ #5
>  | Hardware name: Raspberry Pi Compute Module 4 Rev 1.0 (DT)
>  | Call trace:
>  |  dump_backtrace.part.0+0x1dc/0x1ec
>  |  show_stack+0x24/0x80
>  |  dump_stack_lvl+0x8c/0xb8
>  |  dump_stack+0x1c/0x38
>  |  create_object.isra.0+0x490/0x4b0
>  |  kmemleak_alloc+0x3c/0x50
>  |  kmem_cache_alloc+0x2f8/0x450
>  |  __proc_create+0x18c/0x400
>  |  proc_create_reg+0x54/0xd0
>  |  proc_create_seq_private+0x94/0x120
>  |  init_mm_internals+0x1d8/0x248
>  |  kernel_init_freeable+0x188/0x388
>  |  kernel_init+0x30/0x150
>  |  ret_from_fork+0x10/0x20
>  | kmemleak: Kernel memory leak detector disabled
>  | kmemleak: Object 0xffffff806e24d000 (size 2097152):
>  | kmemleak:   comm "swapper", pid 0, jiffies 4294892296
>  | kmemleak:   min_count = -1
>  | kmemleak:   count = 0
>  | kmemleak:   flags = 0x5
>  | kmemleak:   checksum = 0
>  | kmemleak:   backtrace:
>  |      kmemleak_alloc_phys+0x94/0xb0
>  |      memblock_alloc_range_nid+0x1c0/0x20c
>  |      memblock_alloc_internal+0x88/0x100
>  |      memblock_alloc_try_nid+0x148/0x1ac
>  |      kfence_alloc_pool+0x44/0x6c
>  |      mm_init+0x28/0x98
>  |      start_kernel+0x178/0x3e8
>  |      __primary_switched+0xc4/0xcc
>
> Reported-by: Max Schulze <max.schulze@xxxxxxxxx>
> Fixes: 07313a2b29ed ("mm: kfence: apply kmemleak_ignore_phys on early allocated pool")
> Fixes: 0c24e061196c ("mm: kmemleak: add rbtree and store physical address for objects allocated with PA")
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Yee Lee <yee.lee@xxxxxxxxxxxx>
> ---
>
> Note: This easily reproduces on v5.19, but on 6.0-rc1 the issue is
> hidden by yet more kmemleak changes, but properly freeing the pool is
> the correct thing to do either way, given the post-alloc slab hooks.
> ---
>  mm/kfence/core.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index c252081b11df..9e52f2b87374 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -617,12 +617,13 @@ static bool __init kfence_init_pool_early(void)
>
>         if (!addr) {
>                 /*
> -                * The pool is live and will never be deallocated from this point on.
> -                * Ignore the pool object from the kmemleak phys object tree, as it would
> -                * otherwise overlap with allocations returned by kfence_alloc(), which
> -                * are registered with kmemleak through the slab post-alloc hook.
> +                * The pool is live and will never be deallocated from this
> +                * point on. Remove the pool object from the kmemleak phys
> +                * object tree, as it would otherwise overlap with allocations
> +                * returned by kfence_alloc(), which are registered with
> +                * kmemleak through the slab post-alloc hook.
>                  */
> -               kmemleak_ignore_phys(__pa(__kfence_pool));
> +               kmemleak_free_part_phys(__pa(__kfence_pool), KFENCE_POOL_SIZE);
>                 return true;
>         }
>
> --
> 2.37.1.595.g718a3a8f04-goog
>