From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH] bpf: convert hashtab lock to raw lock Date: Mon, 2 Nov 2015 09:59:27 +0100 (CET) Message-ID: References: <1446243386-26582-1-git-send-email-yang.shi@linaro.org> <20151031000356.GA28070@Alexeis-MacBook-Pro.local> <20151031094736.494427d7@grimm.local.home> <20151101225620.GA28272@Alexeis-MacBook-Pro.local> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Steven Rostedt , 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: Alexei Starovoitov Return-path: In-Reply-To: <20151101225620.GA28272@Alexeis-MacBook-Pro.local> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sun, 1 Nov 2015, Alexei Starovoitov wrote: > 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. I'm working on a document. Thanks, tglx