Re: [PATCH] mm/kmsan: Fix kmsan kmalloc hook when no stack depots are allocated yet

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 30 Sep 2025 13:56:01 +0200 Aleksei Nikiforov <aleksei.nikiforov@linux.ibm.com> wrote:

> If no stack depot is allocated yet,
> due to masking out __GFP_RECLAIM flags
> kmsan called from kmalloc cannot allocate stack depot.
> kmsan fails to record origin and report issues.
> 
> Reusing flags from kmalloc without modifying them should be safe for kmsan.
> For example, such chain of calls is possible:
> test_uninit_kmalloc -> kmalloc -> __kmalloc_cache_noprof ->
> slab_alloc_node -> slab_post_alloc_hook ->
> kmsan_slab_alloc -> kmsan_internal_poison_memory.
> 
> Only when it is called in a context without flags present
> should __GFP_RECLAIM flags be masked.
> 
> With this change all kmsan tests start working reliably.

I'm not seeing reports of "hey, kmsan is broken", so I assume this
failure only occurs under special circumstances?

Please explain how you're triggering this failure and whether you think
we should backport the fix into -stable kernels and if so, are you able
to identify a suitable Fixes: target?

Thanks.