Re: [PATCH] mm/mempolicy: Fix sleeping allocation in alloc_pages_bulk_weighted_interleave()

[Gregory Price <gourry@gourry.net>]

On Fri, Aug 21, 2026 at 05:04:07PM +0000, Eric Dumazet wrote:
> syzbot reported a sleeping function called from invalid context splat
> in bucket_table_alloc().
> 
> When rhashtable_insert_slow() rehashes the table under rcu_read_lock(),
> it calls bucket_table_alloc(..., GFP_ATOMIC | __GFP_NOWARN).
> If the bucket table allocation uses vmalloc, __vmalloc_node_range_noprof()
> invokes vm_area_alloc_pages() -> alloc_pages_bulk_mempolicy_noprof() with
> the passed GFP_ATOMIC flags.
> 
> If the current task has an MPOL_WEIGHTED_INTERLEAVE mempolicy,
> alloc_pages_bulk_weighted_interleave() is called and currently hardcodes
> GFP_KERNEL when allocating the temporary weights array, triggering
> a might_alloc() splat in atomic/RCU contexts.
> 
> Pass the gfp flags (masked with GFP_RECLAIM_MASK to strip page-allocator
> zone modifiers like __GFP_HIGHMEM) received by
> alloc_pages_bulk_weighted_interleave() to kmalloc() instead of
> hardcoding GFP_KERNEL. Since the weights buffer is immediately
> initialized in full, kmalloc() is sufficient.
> 
> Fixes: fa3bea4e1f82 ("mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving")
> Reported-by: syzbot+0dbf6d295b3350944f0b@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/lkml/6a88837e.ae6ddae5.3da009.0040.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Yup, seems a solid oversight on my part.

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

~Gregory