linux-kernel - [PATCH lib] lib: alloc_tag_module_unload must wait for pending kfree

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Message-ID: <20241007205236.11847-1-fw@strlen.de>
Date: Mon,  7 Oct 2024 22:52:24 +0200
From: Florian Westphal <fw@...len.de>
To: linux-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org,
	Florian Westphal <fw@...len.de>,
	Uladzislau Rezki <urezki@...il.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Ben Greear <greearb@...delatech.com>
Subject: [PATCH lib] lib: alloc_tag_module_unload must wait for pending kfree_rcu calls

Ben Greear reports following splat:
 ------------[ cut here ]------------
 net/netfilter/nf_nat_core.c:1114 module nf_nat func:nf_nat_register_fn has 256 allocated at module unload
 WARNING: CPU: 1 PID: 10421 at lib/alloc_tag.c:168 alloc_tag_module_unload+0x22b/0x3f0
 Modules linked in: nf_nat(-) btrfs ufs qnx4 hfsplus hfs minix vfat msdos fat
...
 Hardware name: Default string Default string/SKYBAY, BIOS 5.12 08/04/2020
 RIP: 0010:alloc_tag_module_unload+0x22b/0x3f0
  codetag_unload_module+0x19b/0x2a0
  ? codetag_load_module+0x80/0x80

nf_nat module exit calls kfree_rcu on those addresses, but the free
operation is likely still pending by the time alloc_tag checks for leaks.

Wait for outstanding kfree_rcu operations to complete before checking
resolves this warning.

Reproducer:
unshare -n iptables-nft -t nat -A PREROUTING -p tcp
grep nf_nat /proc/allocinfo # will list 4 allocations
rmmod nft_chain_nat
rmmod nf_nat                # will WARN.

Cc: Uladzislau Rezki <urezki@...il.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Reported-by: Ben Greear <greearb@...delatech.com>
Closes: https://lore.kernel.org/netdev/bdaaef9d-4364-4171-b82b-bcfc12e207eb@candelatech.com/
Fixes: a473573964e5 ("lib: code tagging module support")
Signed-off-by: Florian Westphal <fw@...len.de>
---
 lib/codetag.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/codetag.c b/lib/codetag.c
index afa8a2d4f317..a3472d428821 100644
--- a/lib/codetag.c
+++ b/lib/codetag.c
@@ -228,6 +228,8 @@ bool codetag_unload_module(struct module *mod)
 	if (!mod)
 		return true;
 
+	kvfree_rcu_barrier();
+
 	mutex_lock(&codetag_lock);
 	list_for_each_entry(cttype, &codetag_types, link) {
 		struct codetag_module *found = NULL;
-- 
2.45.2