linux-kernel - [PATCH mm] mm: fix BUG with kvzalloc+GFP

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Date:   Fri, 23 Sep 2022 12:38:58 +0200
From:   Florian Westphal <fw@...len.de>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, vbabka@...e.cz, mhocko@...e.com,
        akpm@...ux-foundation.org, urezki@...il.com,
        <netdev@...r.kernel.org>, <netfilter-devel@...r.kernel.org>,
        Florian Westphal <fw@...len.de>,
        Martin Zaharinov <micron10@...il.com>
Subject: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC

Martin Zaharinov reports BUG() in mm land for 5.19.10 kernel:
 kernel BUG at mm/vmalloc.c:2437!
 invalid opcode: 0000 [#1] SMP
 CPU: 28 PID: 0 Comm: swapper/28 Tainted: G        W  O      5.19.9 #1
 [..]
 RIP: 0010:__get_vm_area_node+0x120/0x130
  __vmalloc_node_range+0x96/0x1e0
  kvmalloc_node+0x92/0xb0
  bucket_table_alloc.isra.0+0x47/0x140
  rhashtable_try_insert+0x3a4/0x440
  rhashtable_insert_slow+0x1b/0x30
 [..]

bucket_table_alloc uses kvzallocGPF_ATOMIC).  If kmalloc fails, this now
falls through to vmalloc and hits code paths that assume GFP_KERNEL.

Revert the problematic change and stay with slab allocator.

Reported-by: Martin Zaharinov <micron10@...il.com>
Fixes: a421ef303008 ("mm: allow !GFP_KERNEL allocations for kvmalloc")
Cc: Michal Hocko <mhocko@...e.com>
Link: https://lore.kernel.org/netdev/09BE0B8A-3ADF-458E-B75E-931B74996355@gmail.com/T/#u

Signed-off-by: Florian Westphal <fw@...len.de>
---
 mm/util.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/util.c b/mm/util.c
index c9439c66d8cf..ba7fe1cb6846 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -593,6 +593,13 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
 	gfp_t kmalloc_flags = flags;
 	void *ret;

+	/*
+	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
+	 * so the given set of flags has to be compatible.
+	 */
+	if ((flags & GFP_KERNEL) != GFP_KERNEL)
+		return kmalloc_node(size, flags, node);
+
 	/*
 	 * We want to attempt a large physically contiguous block first because
 	 * it is less likely to fragment multiple larger blocks and therefore
-- 
2.35.1