From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
Michael Neuling <mikey@neuling.org>,
Paul Mackerras <paulus@samba.org>, Jiri Olsa <jolsa@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jan Stancek <jstancek@redhat.com>
Subject: Re: [PATCH] perf powerpc: Don't call perf_event_disable from atomic context
Date: Mon, 3 Oct 2016 15:47:40 +0200 [thread overview]
Message-ID: <20161003134740.GC3117@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20161003132932.GA28947@krava>
On Mon, Oct 03, 2016 at 03:29:32PM +0200, Jiri Olsa wrote:
> On Fri, Sep 23, 2016 at 06:37:47PM +0200, Peter Zijlstra wrote:
> > On Wed, Sep 21, 2016 at 03:55:34PM +0200, Jiri Olsa wrote:
> > > The trinity syscall fuzzer triggered following WARN on powerpc:
> > > WARNING: CPU: 9 PID: 2998 at arch/powerpc/kernel/hw_breakpoint.c:278
> > > ...
> > > NIP [c00000000093aedc] .hw_breakpoint_handler+0x28c/0x2b0
> > > LR [c00000000093aed8] .hw_breakpoint_handler+0x288/0x2b0
> > > Call Trace:
> > > [c0000002f7933580] [c00000000093aed8] .hw_breakpoint_handler+0x288/0x2b0 (unreliable)
> > > [c0000002f7933630] [c0000000000f671c] .notifier_call_chain+0x7c/0xf0
> > > [c0000002f79336d0] [c0000000000f6abc] .__atomic_notifier_call_chain+0xbc/0x1c0
> > > [c0000002f7933780] [c0000000000f6c40] .notify_die+0x70/0xd0
> > > [c0000002f7933820] [c00000000001a74c] .do_break+0x4c/0x100
> > > [c0000002f7933920] [c0000000000089fc] handle_dabr_fault+0x14/0x48
> > >
> > > Followed by lockdep warning:
> > > ===============================
> > > [ INFO: suspicious RCU usage. ]
> > > 4.8.0-rc5+ #7 Tainted: G W
> > > -------------------------------
> > > ./include/linux/rcupdate.h:556 Illegal context switch in RCU read-side critical section!
> > >
> > > other info that might help us debug this:
> > >
> > > rcu_scheduler_active = 1, debug_locks = 0
> > > 2 locks held by ls/2998:
> > > #0: (rcu_read_lock){......}, at: [<c0000000000f6a00>] .__atomic_notifier_call_chain+0x0/0x1c0
> > > #1: (rcu_read_lock){......}, at: [<c00000000093ac50>] .hw_breakpoint_handler+0x0/0x2b0
> > >
> > > stack backtrace:
> > > CPU: 9 PID: 2998 Comm: ls Tainted: G W 4.8.0-rc5+ #7
> > > Call Trace:
> > > [c0000002f7933150] [c00000000094b1f8] .dump_stack+0xe0/0x14c (unreliable)
> > > [c0000002f79331e0] [c00000000013c468] .lockdep_rcu_suspicious+0x138/0x180
> > > [c0000002f7933270] [c0000000001005d8] .___might_sleep+0x278/0x2e0
> > > [c0000002f7933300] [c000000000935584] .mutex_lock_nested+0x64/0x5a0
> > > [c0000002f7933410] [c00000000023084c] .perf_event_ctx_lock_nested+0x16c/0x380
> > > [c0000002f7933500] [c000000000230a80] .perf_event_disable+0x20/0x60
> > > [c0000002f7933580] [c00000000093aeec] .hw_breakpoint_handler+0x29c/0x2b0
> > > [c0000002f7933630] [c0000000000f671c] .notifier_call_chain+0x7c/0xf0
> > > [c0000002f79336d0] [c0000000000f6abc] .__atomic_notifier_call_chain+0xbc/0x1c0
> > > [c0000002f7933780] [c0000000000f6c40] .notify_die+0x70/0xd0
> > > [c0000002f7933820] [c00000000001a74c] .do_break+0x4c/0x100
> > > [c0000002f7933920] [c0000000000089fc] handle_dabr_fault+0x14/0x48
> > >
> >
> > Well, that lockdep warning only says you should not be taking sleeping
> > locks while holding rcu_read_lock(), which is true. It does not say the
> > context you're doing this is cannot sleep.
> >
> > I'm not familiar enough with the PPC stuff to tell if the DIE_DABR_MATCH
> > trap context is atomic or not and this Changelog doesn't tell me.
> >
> > Anybody?
>
> ping
So I think all the DIE notifiers are atomic, which means this would
indeed be the thing to do. That said, I didn't see anything similar on
other BP implementations.
So it would be good to also explain why PPC needs this in the first
place.
next prev parent reply other threads:[~2016-10-03 13:47 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 13:55 [PATCH] perf powerpc: Don't call perf_event_disable from atomic context Jiri Olsa
2016-09-23 16:37 ` Peter Zijlstra
2016-10-03 13:29 ` Jiri Olsa
2016-10-03 13:47 ` Peter Zijlstra [this message]
2016-10-04 4:29 ` Michael Ellerman
2016-10-04 7:06 ` Peter Zijlstra
2016-10-10 13:19 ` Will Deacon
2016-10-05 8:09 ` Jiri Olsa
2016-10-05 19:53 ` Jiri Olsa
2016-10-06 7:24 ` Peter Zijlstra
2016-10-06 12:33 ` [PATCHv2] " Jiri Olsa
2016-10-24 12:26 ` Peter Zijlstra
2016-10-24 15:49 ` Jiri Olsa
2016-10-25 6:40 ` [perf powerpc] 18d1796d0b: [No primary change] kernel test robot
2016-10-25 6:40 ` [lkp] " kernel test robot
2016-10-25 9:06 ` Peter Zijlstra
2016-10-25 9:06 ` [lkp] " Peter Zijlstra
2016-10-26 2:09 ` Huang, Ying
2016-10-26 2:09 ` [LKP] [lkp] " Huang, Ying
2016-10-26 9:48 ` [PATCHv3] perf powerpc: Don't call perf_event_disable from atomic context Jiri Olsa
2016-10-26 9:48 ` Jiri Olsa
2016-10-26 15:12 ` Peter Zijlstra
2016-10-26 15:12 ` Peter Zijlstra
2016-10-26 15:24 ` Jiri Olsa
2016-10-26 15:24 ` Jiri Olsa
2016-10-28 10:10 ` [tip:perf/urgent] perf/powerpc: Don't call perf_event_disable() " tip-bot for Jiri Olsa
2016-10-04 4:08 ` [PATCH] perf powerpc: Don't call perf_event_disable " Michael Ellerman
2016-10-05 8:08 ` Jiri Olsa
2016-10-05 8:21 ` Jan Stancek
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