netdev - [PATCH] bpf: test_run: Fix timer mode initialization to NO

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Message-ID: <20251006054320.159321-1-chandna.linuxkernel@gmail.com>
Date: Mon,  6 Oct 2025 11:13:20 +0530
From: Sahil Chandna <chandna.linuxkernel@...il.com>
To: ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	song@...nel.org,
	john.fastabend@...il.com,
	haoluo@...gle.com,
	jolsa@...nel.org,
	bpf@...r.kernel.org,
	netdev@...r.kernel.org
Cc: david.hunter.linux@...il.com,
	skhan@...uxfoundation.org,
	khalid@...nel.org,
	Sahil Chandna <chandna.linuxkernel@...il.com>,
	syzbot+1f1fbecb9413cdbfbef8@...kaller.appspotmail.com
Subject: [PATCH] bpf: test_run: Fix timer mode initialization to NO_MIGRATE mode

By default, the timer mode is being initialized to `NO_PREEMPT`.
This disables preemption and forces execution in atomic context.
This can cause issue with PREEMPT_RT when calling spin_lock_bh() due
to sleeping nature of the lock.
...
BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 6107, name: syz.0.17
preempt_count: 1, expected: 0
RCU nest depth: 1, expected: 1
Preemption disabled at:
[<ffffffff891fce58>] bpf_test_timer_enter+0xf8/0x140 net/bpf/test_run.c:42
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 __might_resched+0x44b/0x5d0 kernel/sched/core.c:8957
 __rt_spin_lock kernel/locking/spinlock_rt.c:48 [inline]
 rt_spin_lock+0xc7/0x2c0 kernel/locking/spinlock_rt.c:57
 spin_lock_bh include/linux/spinlock_rt.h:88 [inline]
 __sock_map_delete net/core/sock_map.c:421 [inline]
 sock_map_delete_elem+0xb7/0x170 net/core/sock_map.c:452
 bpf_prog_2c29ac5cdc6b1842+0x43/0x4b
 bpf_dispatcher_nop_func include/linux/bpf.h:1332 [inline]
...
Change initialization to NO_MIGRATE mode to prevent this.

Reported-by: syzbot+1f1fbecb9413cdbfbef8@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1f1fbecb9413cdbfbef8
Tested-by: syzbot+1f1fbecb9413cdbfbef8@...kaller.appspotmail.com
Signed-off-by: Sahil Chandna <chandna.linuxkernel@...il.com>
---
 net/bpf/test_run.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 4a862d605386..daf966dfed69 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1368,7 +1368,7 @@ int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
 				     const union bpf_attr *kattr,
 				     union bpf_attr __user *uattr)
 {
-	struct bpf_test_timer t = { NO_PREEMPT };
+	struct bpf_test_timer t = { NO_MIGRATE };
 	u32 size = kattr->test.data_size_in;
 	struct bpf_flow_dissector ctx = {};
 	u32 repeat = kattr->test.repeat;
@@ -1436,7 +1436,7 @@ int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
 int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog, const union bpf_attr *kattr,
 				union bpf_attr __user *uattr)
 {
-	struct bpf_test_timer t = { NO_PREEMPT };
+	struct bpf_test_timer t = { NO_MIGRATE };
 	struct bpf_prog_array *progs = NULL;
 	struct bpf_sk_lookup_kern ctx = {};
 	u32 repeat = kattr->test.repeat;
-- 
2.50.1