Messages in this thread | | | Date | Mon, 2 Dec 2019 11:24:37 +0900 | From | Masami Hiramatsu <> | Subject | Re: next-20191122: qemu arm64: WARNING: suspicious RCU usage |
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Hello,
Sorry for replying so late.
On Fri, 22 Nov 2019 22:43:56 +0100 Anders Roxell <anders.roxell@linaro.org> 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 <mhiramat@kernel.org>
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