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Date: Sat, 31 Oct 2015 19:37:58 +0100 From: Daniel Borkmann <daniel@...earbox.net> To: Steven Rostedt <rostedt@...dmis.org>, Alexei Starovoitov <alexei.starovoitov@...il.com> CC: Yang Shi <yang.shi@...aro.org>, ast@...nel.org, linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org, netdev@...r.kernel.org, linaro-kernel@...ts.linaro.org Subject: Re: [PATCH] bpf: convert hashtab lock to raw lock On 10/31/2015 02:47 PM, Steven Rostedt wrote: > On Fri, 30 Oct 2015 17:03:58 -0700 > Alexei Starovoitov <alexei.starovoitov@...il.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. ) > 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. Thanks, Daniel -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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