Re: [PATCH 5.19.y] Revert "mm: kfence: apply kmemleak_ignore_phys on early allocated pool"

[Marco Elver <elver@google.com>]

On Tue, 16 Aug 2022 at 18:37, Marco Elver <elver@google.com> wrote:
>
> This reverts commit 07313a2b29ed1079eaa7722624544b97b3ead84b.
>
> Commit 0c24e061196c21d5 ("mm: kmemleak: add rbtree and store physical
> address for objects allocated with PA") is not yet in 5.19 (but appears
> in 6.0). Without 0c24e061196c21d5, kmemleak still stores phys objects
> and non-phys objects in the same tree, and ignoring (instead of freeing)
> will cause insertions into the kmemleak object tree by the slab
> post-alloc hook to conflict with the pool object (see comment).
>
> Reports such as the following would appear on boot, and effectively
> disable kmemleak:
>
>  | 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@online.de>
> Signed-off-by: Marco Elver <elver@google.com>

The discussion is:

Link: https://lore.kernel.org/all/b33b33bc-2d06-1bcd-2df7-43678962b728@online.de/

> ---
>  mm/kfence/core.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 6aff49f6b79e..4b5e5a3d3a63 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -603,6 +603,14 @@ static unsigned long kfence_init_pool(void)
>                 addr += 2 * PAGE_SIZE;
>         }
>
> +       /*
> +        * The pool is live and will never be deallocated from this point on.
> +        * Remove the pool object from the kmemleak 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_free(__kfence_pool);
> +
>         return 0;
>  }
>
> @@ -615,16 +623,8 @@ static bool __init kfence_init_pool_early(void)
>
>         addr = kfence_init_pool();
>
> -       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.
> -                */
> -               kmemleak_ignore_phys(__pa(__kfence_pool));
> +       if (!addr)
>                 return true;
> -       }
>
>         /*
>          * Only release unprotected pages, and do not try to go back and change
> --
> 2.37.1.595.g718a3a8f04-goog
>