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From: peterz@infradead.org
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	linux-kernel@vger.kernel.org, Eddy_Wu@trendmicro.com,
	x86@kernel.org, davem@davemloft.net, rostedt@goodmis.org,
	naveen.n.rao@linux.ibm.com, anil.s.keshavamurthy@intel.com,
	linux-arch@vger.kernel.org, cameron@moodycamel.com,
	oleg@redhat.com, will@kernel.org, paulmck@kernel.org
Subject: Re: [PATCH v5 00/21] kprobes: Unify kretprobe trampoline handlers and make kretprobe lockless
Date: Wed, 2 Sep 2020 15:42:52 +0200	[thread overview]
Message-ID: <20200902134252.GH1362448@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200902221926.f5cae5b4ad00b8d8f9ad99c7@kernel.org>

On Wed, Sep 02, 2020 at 10:19:26PM +0900, Masami Hiramatsu wrote:
> On Wed, 2 Sep 2020 11:36:13 +0200
> peterz@infradead.org wrote:
> 
> > On Wed, Sep 02, 2020 at 05:17:55PM +0900, Masami Hiramatsu wrote:
> > 
> > > > Ok, but then lockdep will yell at you if you have that enabled and run
> > > > the unoptimized things.
> > > 
> > > Oh, does it warn for all spinlock things in kprobes if it is unoptimized?
> > > Hmm, it has to be noted in the documentation.
> > 
> > Lockdep will warn about spinlocks used in NMI context that are also used
> > outside NMI context.
> 
> OK, but raw_spin_lock_irqsave() will not involve lockdep, correct?

It will. The distinction between spin_lock and raw_spin_lock is only
that raw_spin_lock stays a spinlock on PREEMPT_RT, while spin_lock will
turn into a (PI) mutex in that case.

But both will call into lockdep. Unlike local_irq_disable() and
raw_local_irq_disable(), where the latter will not. Yes your prefixes
are a mess :/

> > Now, for the kretprobe that kprobe_busy flag prevents the actual
> > recursion self-deadlock, but lockdep isn't smart enough to see that.
> > 
> > One way around this might be to use SINGLE_DEPTH_NESTING for locks when
> > we use them from INT3 context. That way they'll have a different class
> > and lockdep will not see the recursion.
> 
> Hmm, so lockdep warns only when it detects the spinlock in NMI context,
> and int3 is now always NMI, thus all spinlock (except raw_spinlock?)
> in kprobe handlers should get warned, right?
> I have tested this series up to [16/21] with optprobe disabled, but
> I haven't see the lockdep warnings.

There's a bug, that might make it miss it. I have a patch. I'll send it
shortly.

> > pre_handler_kretprobe() is always called from INT3, right?
> 
> No, not always, it can be called from optprobe (same as original code
> context) or ftrace handler.
> But if you set 0 to /proc/sys/debug/kprobe_optimization, and compile
> the kernel without function tracer, it should always be called from
> INT3.

D'oh, ofcourse! Arguably I should make the optprobe context NMI like
too.. but that's for another day.

  reply	other threads:[~2020-09-02 13:50 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-29 12:59 [PATCH v5 00/21] kprobes: Unify kretprobe trampoline handlers and make kretprobe lockless Masami Hiramatsu
2020-08-29 13:00 ` [PATCH v5 01/21] kprobes: Add generic kretprobe trampoline handler Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:00 ` [PATCH v5 02/21] x86/kprobes: Use " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:00 ` [PATCH v5 03/21] arm: kprobes: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:00 ` [PATCH v5 04/21] arm64: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:00 ` [PATCH v5 05/21] arc: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:00 ` [PATCH v5 06/21] csky: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:01 ` [PATCH v5 07/21] ia64: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:01 ` [PATCH v5 08/21] mips: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:01 ` [PATCH v5 09/21] parisc: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:01 ` [PATCH v5 10/21] powerpc: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:02 ` [PATCH v5 11/21] s390: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:02 ` [PATCH v5 12/21] sh: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:02 ` [PATCH v5 13/21] sparc: " Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-08-29 13:02 ` [PATCH v5 14/21] kprobes: Remove NMI context check Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] " tip-bot2 for Masami Hiramatsu
2020-10-31  1:38   ` [PATCH v5 14/21] " Steven Rostedt
2020-11-02  5:11     ` Masami Hiramatsu
2020-11-02  5:53       ` Masami Hiramatsu
2020-11-02  7:02         ` Masami Hiramatsu
2020-11-02 14:27           ` Steven Rostedt
2020-11-03  5:39             ` Masami Hiramatsu
2020-11-03 16:09               ` Steven Rostedt
2020-11-04  2:08                 ` Masami Hiramatsu
2020-11-04 14:47                   ` Steven Rostedt
2020-11-05  5:15                     ` Masami Hiramatsu
2020-08-29 13:02 ` [PATCH v5 15/21] kprobes: Free kretprobe_instance with rcu callback Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] kprobes: Free kretprobe_instance with RCU callback tip-bot2 for Masami Hiramatsu
2020-08-29 13:03 ` [PATCH v5 16/21] kprobes: Make local used functions static Masami Hiramatsu
2020-09-14 17:16   ` [tip: perf/kprobes] kprobes: Make local " tip-bot2 for Masami Hiramatsu
2020-08-29 13:03 ` [PATCH v5 17/21] llist: Add nonatomic __llist_add() and __llist_dell_all() Masami Hiramatsu
2020-10-12 16:24   ` Ingo Molnar
2020-10-14  0:24     ` Masami Hiramatsu
2020-10-12 17:08   ` [tip: perf/kprobes] " tip-bot2 for Peter Zijlstra
2020-08-29 13:03 ` [PATCH v5 18/21] kprobes: Remove kretprobe hash Masami Hiramatsu
2020-10-12 17:08   ` [tip: perf/kprobes] " tip-bot2 for Peter Zijlstra
2020-08-29 13:03 ` [PATCH v5 19/21] asm-generic/atomic: Add try_cmpxchg() fallbacks Masami Hiramatsu
2020-10-12 16:25   ` Ingo Molnar
2020-10-12 17:08   ` [tip: perf/kprobes] " tip-bot2 for Peter Zijlstra
2020-08-29 13:03 ` [PATCH v5 20/21] freelist: Lock less freelist Masami Hiramatsu
2020-10-12 17:08   ` [tip: perf/kprobes] freelist: Implement lockless freelist tip-bot2 for Peter Zijlstra
2020-08-29 13:03 ` [PATCH v5 21/21] kprobes: Replace rp->free_instance with freelist Masami Hiramatsu
2020-10-12 17:08   ` [tip: perf/kprobes] " tip-bot2 for Peter Zijlstra
2020-09-01 19:08 ` [PATCH v5 00/21] kprobes: Unify kretprobe trampoline handlers and make kretprobe lockless Peter Zijlstra
2020-09-02  0:37   ` Masami Hiramatsu
2020-09-02  7:02     ` peterz
2020-09-02  8:17       ` Masami Hiramatsu
2020-09-02  9:36         ` peterz
2020-09-02 13:19           ` Masami Hiramatsu
2020-09-02 13:42             ` peterz [this message]
2020-09-03  1:39               ` Masami Hiramatsu
2020-09-03  2:02                 ` Masami Hiramatsu
2020-09-07 17:44                   ` Frank Ch. Eigler
2020-09-08  2:55                     ` Masami Hiramatsu
2020-09-08 10:37                 ` peterz
2020-09-08 11:15                   ` Eddy_Wu
2020-09-08 11:33                     ` peterz
2020-09-08 15:09                   ` Masami Hiramatsu
2020-09-09  5:28                     ` Masami Hiramatsu
2020-09-11  2:32       ` Masami Hiramatsu

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