Hi,
I'm seeing the following warning when I'm booting an arm64 allmodconfig
kernel [1] on linux-next; tag next-20191122, is this anything you've seen
before ?
The code seems to have introduced a long time ago and the warning was
added recently 28875945ba98 ("rcu: Add support for consolidated-RCU
reader checking").
[ 193.853316][ T1] Kprobe smoke test: started
[ 193.898283][ T1]
[ 193.899587][ T1] =============================
[ 193.901777][ T1] WARNING: suspicious RCU usage
[ 193.903518][ T1] 5.4.0-rc8-next-20191122-00015-gaf188dd3de19 #1
Not tainted
[ 193.906423][ T1] -----------------------------
[ 193.908214][ T1] kernel/kprobes.c:329 RCU-list traversed in
non-reader section!!
[ 193.911189][ T1]
[ 193.911189][ T1] other info that might help us debug this:
[ 193.911189][ T1]
[ 193.914972][ T1]
[ 193.914972][ T1] rcu_scheduler_active = 2, debug_locks = 1
[ 193.918084][ T1] 1 lock held by swapper/0/1:
[ 193.919774][ T1] #0: ffffa00014255a30 (kprobe_mutex){+.+.}, at:
register_kprobe+0xa0/0xb28
[ 193.923346][ T1]
[ 193.923346][ T1] stack backtrace:
[ 193.925877][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
5.4.0-rc8-next-20191122-00015-gaf188dd3de19 #1
[ 193.929388][ T1] Hardware name: linux,dummy-virt (DT)
[ 193.931247][ T1] Call trace:
[ 193.932516][ T1] dump_backtrace+0x0/0x2d0
[ 193.933989][ T1] show_stack+0x28/0x38
[ 193.935375][ T1] dump_stack+0x1e8/0x28c
[ 193.936935][ T1] lockdep_rcu_suspicious+0xf4/0x108
[ 193.938727][ T1] get_kprobe+0xe0/0x188
[ 193.940251][ T1] __get_valid_kprobe+0x30/0x168
[ 193.941937][ T1] register_kprobe+0xa8/0xb28
[ 193.943541][ T1] init_test_probes+0xf8/0x548
[ 193.945220][ T1] run_init_test_probes+0x6c/0xa0
[ 193.946946][ T1] do_one_initcall+0x4c8/0xae8
[ 193.948646][ T1] kernel_init_freeable+0x3e8/0x508
[ 193.950393][ T1] kernel_init+0x1c/0x208
[ 193.951940][ T1] ret_from_fork+0x10/0x18
[ 194.367780][ T1] Kprobe smoke test: passed successfully
Cheers,
Anders
[1] http://people.linaro.org/~anders.roxell/kernel_config-next-20191122.config
Hello,
Sorry for replying so late.
On Fri, 22 Nov 2019 22:43:56 +0100
Anders Roxell <[email protected]> wrote:
> Hi,
>
> I'm seeing the following warning when I'm booting an arm64 allmodconfig
> kernel [1] on linux-next; tag next-20191122, is this anything you've seen
> before ?
>
> The code seems to have introduced a long time ago and the warning was
> added recently 28875945ba98 ("rcu: Add support for consolidated-RCU
> reader checking").
I've never seen this but the warning itself is justified.
struct kprobe *get_kprobe(void *addr)
{
struct hlist_head *head;
struct kprobe *p;
head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
hlist_for_each_entry_rcu(p, head, hlist) { <---- this cause the warning
if (p->addr == addr)
return p;
}
return NULL;
}
The kprobe_table itself is protected by kprobe_mutex OR rcu.
If the caller locks the kprobe_mutex, we can safely access the hash
table, this is what the register_kprobe does. If not, the caller must
disable preemption, this happens when a kprobe (breakpoint) is hit.
Thus, the kernel itself is safe, but it should be fixed.
Thank you,
--
Masami Hiramatsu <[email protected]>