Re: [PATCH] mm/zone_device: Do not touch device folio after calling ->folio_free()

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Apr 10, 2026 at 04:03:46PM -0700, Matthew Brost wrote:
> The contents of a device folio can immediately change after calling
> ->folio_free(), as the folio may be reallocated by a driver with a
> different order. Instead of touching the folio again to extract the
> pgmap, use the local stack variable when calling percpu_ref_put_many().
> 
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Balbir Singh <balbirs@nvidia.com>
> Cc: linux-mm@kvack.org
> Cc: linux-cxl@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org

Cc: <stable@vger.kernel.org>

> Fixes: d245f9b4ab80 ("mm/zone_device: support large zone device private folios")
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> 
> ---
> Stack trace:
> 
> [  631.875165] [IGT] xe_exec_system_allocator: starting subtest threads-many-new-prefetch
> [  632.282992] Oops: general protection fault, probably for non-canonical address 0x900000000000000: 0000 [#1] SMP NOPTI
> [  632.293469] CPU: 8 UID: 0 PID: 59267 Comm: xe_exec_system_ Not tainted 7.0.0-rc7-xe+ #281 PREEMPT(full)
> [  632.316023] RIP: 0010:free_zone_device_folio+0x149/0x240
> [  632.339782] RSP: 0000:ffffc90023d1fd00 EFLAGS: 00010206
> [  632.344947] RAX: 0900000000000000 RBX: 0000000000000001 RCX: 0000000094472d4d
> [  632.351991] RDX: ffffffff8155c76f RSI: 000000006f2213bf RDI: 000000008e84943a
> [  632.359042] RBP: ffffea0ff4030001 R08: 0000000000000000 R09: 0000000000000001
> [  632.366094] R10: 0000000000000028 R11: 0000000000000000 R12: ffff88811828e400
> [  632.373145] R13: 0000000000000000 R14: 000fffffc0000000 R15: 0000000000100073
> [  632.380194] FS:  00007f2f0fdfe6c0(0000) GS:ffff88890a7e7000(0000) knlGS:0000000000000000
> [  632.388186] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  632.393870] CR2: 00007f2f002e90f8 CR3: 0000000106708002 CR4: 0000000000f70ef0
> [  632.400919] PKRU: 55555554
> [  632.403605] Call Trace:
> [  632.406039]  <TASK>
> [  632.408131]  do_swap_page+0x146d/0x18c0
> [  632.411938]  ? __pte_offset_map+0x3e/0x190
> [  632.415994]  __handle_mm_fault+0x6e8/0x8d0
> [  632.420053]  handle_mm_fault+0xbf/0x250
> [  632.423855]  ? lock_mm_and_find_vma+0x41/0x6f0
> [  632.428256]  do_user_addr_fault+0x168/0x690
> [  632.432399]  exc_page_fault+0x74/0x200
> [  632.436117]  asm_exc_page_fault+0x26/0x30
> [  632.440092] RIP: 0033:0x5587554ff70d
> [  632.462142] RSP: 002b:00007f2f0fdfc970 EFLAGS: 00010246
> [  632.467308] RAX: 0000000000003fc0 RBX: 00007f2f082e1fc0 RCX: 00007f2f12b3287d
> [  632.474355] RDX: 0000000000000000 RSI: 00000000c048644a RDI: 0000000000000003
> [  632.481404] RBP: 00007f2f082e1fc0 R08: 00007f2f0fdfc958 R09: 0000000000000066
> [  632.488450] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> [  632.495495] R13: 00007f2f082de000 R14: 0000000000c00002 R15: 00007f2f1319e000
> [  632.502547]  </TASK>
> ---
>  mm/memremap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memremap.c b/mm/memremap.c
> index ac7be07e3361..053842d45cb1 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -454,7 +454,7 @@ void free_zone_device_folio(struct folio *folio)
>  		if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->folio_free))
>  			break;
>  		pgmap->ops->folio_free(folio);
> -		percpu_ref_put_many(&folio->pgmap->ref, nr);
> +		percpu_ref_put_many(&pgmap->ref, nr);
>  		break;
>  
>  	case MEMORY_DEVICE_GENERIC:
> -- 
> 2.34.1
>