From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: Re: [PATCH] bpf: convert hashtab lock to raw lock Date: Sun, 1 Nov 2015 14:56:22 -0800 Message-ID: <20151101225620.GA28272@Alexeis-MacBook-Pro.local> References: <1446243386-26582-1-git-send-email-yang.shi@linaro.org> <20151031000356.GA28070@Alexeis-MacBook-Pro.local> <20151031094736.494427d7@grimm.local.home> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Yang Shi , ast@kernel.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, netdev@vger.kernel.org, linaro-kernel@lists.linaro.org To: Steven Rostedt Return-path: Content-Disposition: inline In-Reply-To: <20151031094736.494427d7@grimm.local.home> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sat, Oct 31, 2015 at 09:47:36AM -0400, Steven Rostedt wrote: > On Fri, 30 Oct 2015 17:03:58 -0700 > Alexei Starovoitov 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:[] 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. I see. The patch makes sense then. Would be good to document this peculiarity of spin_lock.