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mm/mempolicy: fix sleeping allocation in alloc_pages_bulk_weighted_interleave()

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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.

Link: https://lore.kernel.org/20260821170407.3721004-1-edumazet@google.com
Fixes: fa3bea4e1f ("mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot+0dbf6d295b3350944f0b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/6a88837e.ae6ddae5.3da009.0040.GAE@google.com/T/#u
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Eric Dumazet 2026-08-21 17:04:07 +00:00 committed by Andrew Morton
parent fe6cf98493
commit 540e583b66
1 changed files with 1 additions and 1 deletions
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mm/mempolicy.c
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@ -2679,7 +2679,7 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
prev_node = node;
/* create a local copy of node weights to operate on outside rcu */
weights = kzalloc(nr_node_ids, GFP_KERNEL);
weights = kmalloc(nr_node_ids, gfp & GFP_RECLAIM_MASK);
if (!weights)
return total_allocated;