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Date: Fri, 26 May 2017 01:45:02 -0700
From: tip-bot for Thomas Gleixner <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: paulmck@...ux.vnet.ibm.com, peterz@...radead.org, mingo@...nel.org,
bigeasy@...utronix.de, tglx@...utronix.de, mhiramat@...nel.org,
hpa@...or.com, linux-kernel@...r.kernel.org, rostedt@...dmis.org
Subject: [tip:smp/hotplug] kprobes: Cure hotplug lock ordering issues
Commit-ID: 2d1e38f56622b9bb5af85be63c1052c056f5c677
Gitweb: http://git.kernel.org/tip/2d1e38f56622b9bb5af85be63c1052c056f5c677
Author: Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Wed, 24 May 2017 10:15:36 +0200
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 26 May 2017 10:10:45 +0200
kprobes: Cure hotplug lock ordering issues
Converting the cpu hotplug locking to a percpu rwsem unearthed hidden lock
ordering problems.
There is a wide range of locks involved in this: kprobe_mutex,
jump_label_mutex, ftrace_lock, text_mutex, event_mutex, module_mutex,
func_hash->regex_lock and a gazillion of lock order permutations with
nested get_online_cpus() calls.
Some of those permutations are potential deadlocks even with the current
nesting hotplug locking scheme, but they can't be discovered by lockdep.
The conversion of the hotplug locking to a percpu rwsem requires to prevent
nested locking, so it's required to take the hotplug rwsem early in the
call chain and establish a proper lock order.
After quite some analysis and going down the wrong road severa times the
following lock order has been chosen:
kprobe_mutex -> cpus_rwsem -> jump_label_mutex -> text_mutex
For kprobes which hook on an ftrace function trace point, it's required to
drop cpus_rwsem before calling into the ftrace code to avoid a deadlock on
the func_hash->regex_lock.
[ Steven: Ftrace interaction fixes ]
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sebastian Siewior <bigeasy@...utronix.de>
Link: http://lkml.kernel.org/r/20170524081549.104864779@linutronix.de
---
kernel/kprobes.c | 59 ++++++++++++++++++++++++++++++--------------------------
1 file changed, 32 insertions(+), 27 deletions(-)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2d2d3a5..9f60567 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -483,11 +483,6 @@ static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer);
*/
static void do_optimize_kprobes(void)
{
- /* Optimization never be done when disarmed */
- if (kprobes_all_disarmed || !kprobes_allow_optimization ||
- list_empty(&optimizing_list))
- return;
-
/*
* The optimization/unoptimization refers online_cpus via
* stop_machine() and cpu-hotplug modifies online_cpus.
@@ -495,14 +490,19 @@ static void do_optimize_kprobes(void)
* This combination can cause a deadlock (cpu-hotplug try to lock
* text_mutex but stop_machine can not be done because online_cpus
* has been changed)
- * To avoid this deadlock, we need to call get_online_cpus()
+ * To avoid this deadlock, caller must have locked cpu hotplug
* for preventing cpu-hotplug outside of text_mutex locking.
*/
- get_online_cpus();
+ lockdep_assert_cpus_held();
+
+ /* Optimization never be done when disarmed */
+ if (kprobes_all_disarmed || !kprobes_allow_optimization ||
+ list_empty(&optimizing_list))
+ return;
+
mutex_lock(&text_mutex);
arch_optimize_kprobes(&optimizing_list);
mutex_unlock(&text_mutex);
- put_online_cpus();
}
/*
@@ -513,12 +513,13 @@ static void do_unoptimize_kprobes(void)
{
struct optimized_kprobe *op, *tmp;
+ /* See comment in do_optimize_kprobes() */
+ lockdep_assert_cpus_held();
+
/* Unoptimization must be done anytime */
if (list_empty(&unoptimizing_list))
return;
- /* Ditto to do_optimize_kprobes */
- get_online_cpus();
mutex_lock(&text_mutex);
arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
/* Loop free_list for disarming */
@@ -537,7 +538,6 @@ static void do_unoptimize_kprobes(void)
list_del_init(&op->list);
}
mutex_unlock(&text_mutex);
- put_online_cpus();
}
/* Reclaim all kprobes on the free_list */
@@ -562,6 +562,7 @@ static void kick_kprobe_optimizer(void)
static void kprobe_optimizer(struct work_struct *work)
{
mutex_lock(&kprobe_mutex);
+ cpus_read_lock();
/* Lock modules while optimizing kprobes */
mutex_lock(&module_mutex);
@@ -587,6 +588,7 @@ static void kprobe_optimizer(struct work_struct *work)
do_free_cleaned_kprobes();
mutex_unlock(&module_mutex);
+ cpus_read_unlock();
mutex_unlock(&kprobe_mutex);
/* Step 5: Kick optimizer again if needed */
@@ -650,9 +652,8 @@ static void optimize_kprobe(struct kprobe *p)
/* Short cut to direct unoptimizing */
static void force_unoptimize_kprobe(struct optimized_kprobe *op)
{
- get_online_cpus();
+ lockdep_assert_cpus_held();
arch_unoptimize_kprobe(op);
- put_online_cpus();
if (kprobe_disabled(&op->kp))
arch_disarm_kprobe(&op->kp);
}
@@ -791,6 +792,7 @@ static void try_to_optimize_kprobe(struct kprobe *p)
return;
/* For preparing optimization, jump_label_text_reserved() is called */
+ cpus_read_lock();
jump_label_lock();
mutex_lock(&text_mutex);
@@ -812,6 +814,7 @@ static void try_to_optimize_kprobe(struct kprobe *p)
out:
mutex_unlock(&text_mutex);
jump_label_unlock();
+ cpus_read_unlock();
}
#ifdef CONFIG_SYSCTL
@@ -826,6 +829,7 @@ static void optimize_all_kprobes(void)
if (kprobes_allow_optimization)
goto out;
+ cpus_read_lock();
kprobes_allow_optimization = true;
for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
head = &kprobe_table[i];
@@ -833,6 +837,7 @@ static void optimize_all_kprobes(void)
if (!kprobe_disabled(p))
optimize_kprobe(p);
}
+ cpus_read_unlock();
printk(KERN_INFO "Kprobes globally optimized\n");
out:
mutex_unlock(&kprobe_mutex);
@@ -851,6 +856,7 @@ static void unoptimize_all_kprobes(void)
return;
}
+ cpus_read_lock();
kprobes_allow_optimization = false;
for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
head = &kprobe_table[i];
@@ -859,6 +865,7 @@ static void unoptimize_all_kprobes(void)
unoptimize_kprobe(p, false);
}
}
+ cpus_read_unlock();
mutex_unlock(&kprobe_mutex);
/* Wait for unoptimizing completion */
@@ -1010,14 +1017,11 @@ static void arm_kprobe(struct kprobe *kp)
arm_kprobe_ftrace(kp);
return;
}
- /*
- * Here, since __arm_kprobe() doesn't use stop_machine(),
- * this doesn't cause deadlock on text_mutex. So, we don't
- * need get_online_cpus().
- */
+ cpus_read_lock();
mutex_lock(&text_mutex);
__arm_kprobe(kp);
mutex_unlock(&text_mutex);
+ cpus_read_unlock();
}
/* Disarm a kprobe with text_mutex */
@@ -1027,10 +1031,12 @@ static void disarm_kprobe(struct kprobe *kp, bool reopt)
disarm_kprobe_ftrace(kp);
return;
}
- /* Ditto */
+
+ cpus_read_lock();
mutex_lock(&text_mutex);
__disarm_kprobe(kp, reopt);
mutex_unlock(&text_mutex);
+ cpus_read_unlock();
}
/*
@@ -1298,13 +1304,10 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
int ret = 0;
struct kprobe *ap = orig_p;
+ cpus_read_lock();
+
/* For preparing optimization, jump_label_text_reserved() is called */
jump_label_lock();
- /*
- * Get online CPUs to avoid text_mutex deadlock.with stop machine,
- * which is invoked by unoptimize_kprobe() in add_new_kprobe()
- */
- get_online_cpus();
mutex_lock(&text_mutex);
if (!kprobe_aggrprobe(orig_p)) {
@@ -1352,8 +1355,8 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
out:
mutex_unlock(&text_mutex);
- put_online_cpus();
jump_label_unlock();
+ cpus_read_unlock();
if (ret == 0 && kprobe_disabled(ap) && !kprobe_disabled(p)) {
ap->flags &= ~KPROBE_FLAG_DISABLED;
@@ -1555,9 +1558,12 @@ int register_kprobe(struct kprobe *p)
goto out;
}
- mutex_lock(&text_mutex); /* Avoiding text modification */
+ cpus_read_lock();
+ /* Prevent text modification */
+ mutex_lock(&text_mutex);
ret = prepare_kprobe(p);
mutex_unlock(&text_mutex);
+ cpus_read_unlock();
if (ret)
goto out;
@@ -1570,7 +1576,6 @@ int register_kprobe(struct kprobe *p)
/* Try to optimize kprobe */
try_to_optimize_kprobe(p);
-
out:
mutex_unlock(&kprobe_mutex);
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