From: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Eddy_Wu@trendmicro.com, x86@kernel.org, davem@davemloft.net,
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 14/21] kprobes: Remove NMI context check
Date: Mon, 2 Nov 2020 09:27:26 -0500 [thread overview]
Message-ID: <20201102092726.57cb643f@gandalf.local.home> (raw)
In-Reply-To: <20201102160234.fa0ae70915ad9e2b21c08b85@kernel.org>
[ Peter Z, please take a look a this ]
On Mon, 2 Nov 2020 16:02:34 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >From 509b27efef8c7dbf56cab2e812916d6cd778c745 Mon Sep 17 00:00:00 2001
> From: Masami Hiramatsu <mhiramat@kernel.org>
> Date: Mon, 2 Nov 2020 15:37:28 +0900
> Subject: [PATCH] kprobes: Disable lockdep for kprobe busy area
>
> Since the code area in between kprobe_busy_begin()/end() prohibits
> other kprobs to call probe handlers, we can avoid inconsitent
> locks there. But lockdep doesn't know that, so it warns rp->lock
> or kretprobe_table_lock.
>
> To supress those false-positive errors, disable lockdep while
> kprobe_busy is set.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> kernel/kprobes.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 8a12a25fa40d..c7196e583600 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1295,10 +1295,12 @@ void kprobe_busy_begin(void)
> __this_cpu_write(current_kprobe, &kprobe_busy);
> kcb = get_kprobe_ctlblk();
> kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> + lockdep_off();
> }
>
> void kprobe_busy_end(void)
> {
> + lockdep_on();
> __this_cpu_write(current_kprobe, NULL);
> preempt_enable();
> }
> --
No, this is not the correct workaround (too big of a hammer). You could do
the following:
From 4139d9c8437b0bd2262e989ca4eb0a83b7e7bb72 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Mon, 2 Nov 2020 09:17:49 -0500
Subject: [PATCH] kprobes: Tell lockdep about kprobe nesting
Since the kprobe handlers have protection that prohibits other handlers from
executing in other contexts (like if an NMI comes in while processing a
kprobe, and executes the same kprobe, it will get fail with a "busy"
return). Lockdep is unaware of this protection. Use lockdep's nesting api to
differentiate between locks taken in NMI context and other context to
supress the false warnings.
Link: https://lore.kernel.org/r/20201102160234.fa0ae70915ad9e2b21c08b85@kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/kprobes.c | 24 ++++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 8a12a25fa40d..ccb285867059 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1249,7 +1249,12 @@ __acquires(hlist_lock)
*head = &kretprobe_inst_table[hash];
hlist_lock = kretprobe_table_lock_ptr(hash);
- raw_spin_lock_irqsave(hlist_lock, *flags);
+ /*
+ * Nested is a workaround that will soon not be needed.
+ * There's other protections that make sure the same lock
+ * is not taken on the same CPU that lockdep is unaware of.
+ */
+ raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi());
}
NOKPROBE_SYMBOL(kretprobe_hash_lock);
@@ -1258,7 +1263,12 @@ static void kretprobe_table_lock(unsigned long hash,
__acquires(hlist_lock)
{
raw_spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash);
- raw_spin_lock_irqsave(hlist_lock, *flags);
+ /*
+ * Nested is a workaround that will soon not be needed.
+ * There's other protections that make sure the same lock
+ * is not taken on the same CPU that lockdep is unaware of.
+ */
+ raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi());
}
NOKPROBE_SYMBOL(kretprobe_table_lock);
@@ -2025,10 +2035,16 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
struct kretprobe *rp = container_of(p, struct kretprobe, kp);
unsigned long hash, flags = 0;
struct kretprobe_instance *ri;
+ int nmi = !!in_nmi();
/* TODO: consider to only swap the RA after the last pre_handler fired */
hash = hash_ptr(current, KPROBE_HASH_BITS);
- raw_spin_lock_irqsave(&rp->lock, flags);
+ /*
+ * Nested is a workaround that will soon not be needed.
+ * There's other protections that make sure the same lock
+ * is not taken on the same CPU that lockdep is unaware of.
+ */
+ raw_spin_lock_irqsave_nested(&rp->lock, flags, nmi);
if (!hlist_empty(&rp->free_instances)) {
ri = hlist_entry(rp->free_instances.first,
struct kretprobe_instance, hlist);
@@ -2039,7 +2055,7 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
ri->task = current;
if (rp->entry_handler && rp->entry_handler(ri, regs)) {
- raw_spin_lock_irqsave(&rp->lock, flags);
+ raw_spin_lock_irqsave_nested(&rp->lock, flags, nmi);
hlist_add_head(&ri->hlist, &rp->free_instances);
raw_spin_unlock_irqrestore(&rp->lock, flags);
return 0;
--
2.25.4
next prev parent reply other threads:[~2020-11-02 14:27 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 [this message]
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
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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