Messages in this thread | | | Date | Mon, 02 Nov 2015 09:12:29 -0800 | From | "Shi, Yang" <> | Subject | Re: [PATCH] bpf: convert hashtab lock to raw lock |
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On 10/31/2015 11:37 AM, Daniel Borkmann wrote: > On 10/31/2015 02:47 PM, Steven Rostedt wrote: >> On Fri, 30 Oct 2015 17:03:58 -0700 >> Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: >>> On Fri, Oct 30, 2015 at 03:16:26PM -0700, Yang Shi wrote: >>>> When running bpf samples on rt kernel, it reports the below warning: >>>> >>>> BUG: sleeping function called from invalid context at >>>> kernel/locking/rtmutex.c:917 >>>> in_atomic(): 1, irqs_disabled(): 128, pid: 477, name: ping >>>> Preemption disabled at:[<ffff80000017db58>] kprobe_perf_func+0x30/0x228 >>> ... >>>> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c >>>> index 83c209d..972b76b 100644 >>>> --- a/kernel/bpf/hashtab.c >>>> +++ b/kernel/bpf/hashtab.c >>>> @@ -17,7 +17,7 @@ >>>> struct bpf_htab { >>>> struct bpf_map map; >>>> struct hlist_head *buckets; >>>> - spinlock_t lock; >>>> + raw_spinlock_t lock; >>> >>> How do we address such things in general? >>> I bet there are tons of places around the kernel that >>> call spin_lock from atomic. >>> I'd hate to lose the benefits of lockdep of non-raw spin_lock >>> just to make rt happy. >> >> You wont lose any benefits of lockdep. Lockdep still checks >> raw_spin_lock(). The only difference between raw_spin_lock and >> spin_lock is that in -rt spin_lock turns into an rt_mutex() and >> raw_spin_lock stays a spin lock. > > ( Btw, Yang, would have been nice if your commit description would have > already included such info, not only that you convert it, but also why > it's okay to do so. )
I think Thomas's document will include all the information about rt spin lock/raw spin lock, etc.
Alexei & Daniel,
If you think such info is necessary, I definitely could add it into the commit log in v2.
> >> The error is that in -rt, you called a mutex and not a spin lock while >> atomic. > > You are right, I think this happens due to the preempt_disable() in the > trace_call_bpf() handler. So, I think the patch seems okay. The dep_map > is btw union'ed in the struct spinlock case to the same offset of the > dep_map from raw_spinlock. > > It's a bit inconvenient, though, when we add other library code as maps > in future, f.e. things like rhashtable as they would first need to be > converted to raw_spinlock_t as well, but judging from the git log, it > looks like common practice.
Yes, it is common practice for converting sleepable spin lock to raw spin lock in -rt to avoid scheduling in atomic context bug.
Thanks, Yang
> > Thanks, > Daniel
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