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Subject[PATCH AUTOSEL 4.19 29/45] kprobes: Fix potential deadlock in kprobe_optimizer()
Date
From: Andrea Righi <andrea.righi@canonical.com>

[ Upstream commit f1c6ece23729257fb46562ff9224cf5f61b818da ]

lockdep reports the following deadlock scenario:

WARNING: possible circular locking dependency detected

kworker/1:1/48 is trying to acquire lock:
000000008d7a62b2 (text_mutex){+.+.}, at: kprobe_optimizer+0x163/0x290

but task is already holding lock:
00000000850b5e2d (module_mutex){+.+.}, at: kprobe_optimizer+0x31/0x290

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (module_mutex){+.+.}:
__mutex_lock+0xac/0x9f0
mutex_lock_nested+0x1b/0x20
set_all_modules_text_rw+0x22/0x90
ftrace_arch_code_modify_prepare+0x1c/0x20
ftrace_run_update_code+0xe/0x30
ftrace_startup_enable+0x2e/0x50
ftrace_startup+0xa7/0x100
register_ftrace_function+0x27/0x70
arm_kprobe+0xb3/0x130
enable_kprobe+0x83/0xa0
enable_trace_kprobe.part.0+0x2e/0x80
kprobe_register+0x6f/0xc0
perf_trace_event_init+0x16b/0x270
perf_kprobe_init+0xa7/0xe0
perf_kprobe_event_init+0x3e/0x70
perf_try_init_event+0x4a/0x140
perf_event_alloc+0x93a/0xde0
__do_sys_perf_event_open+0x19f/0xf30
__x64_sys_perf_event_open+0x20/0x30
do_syscall_64+0x65/0x1d0
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (text_mutex){+.+.}:
__lock_acquire+0xfcb/0x1b60
lock_acquire+0xca/0x1d0
__mutex_lock+0xac/0x9f0
mutex_lock_nested+0x1b/0x20
kprobe_optimizer+0x163/0x290
process_one_work+0x22b/0x560
worker_thread+0x50/0x3c0
kthread+0x112/0x150
ret_from_fork+0x3a/0x50

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(module_mutex);
lock(text_mutex);
lock(module_mutex);
lock(text_mutex);

*** DEADLOCK ***

As a reproducer I've been using bcc's funccount.py
(https://github.com/iovisor/bcc/blob/master/tools/funccount.py),
for example:

# ./funccount.py '*interrupt*'

That immediately triggers the lockdep splat.

Fix by acquiring text_mutex before module_mutex in kprobe_optimizer().

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: d5b844a2cf50 ("ftrace/x86: Remove possible deadlock between register_kprobe() and ftrace_run_update_code()")
Link: http://lkml.kernel.org/r/20190812184302.GA7010@xps-13
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/kprobes.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 29ff6635d2597..714d63f60460b 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -483,6 +483,7 @@ static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer);
*/
static void do_optimize_kprobes(void)
{
+ lockdep_assert_held(&text_mutex);
/*
* The optimization/unoptimization refers online_cpus via
* stop_machine() and cpu-hotplug modifies online_cpus.
@@ -500,9 +501,7 @@ static void do_optimize_kprobes(void)
list_empty(&optimizing_list))
return;

- mutex_lock(&text_mutex);
arch_optimize_kprobes(&optimizing_list);
- mutex_unlock(&text_mutex);
}

/*
@@ -513,6 +512,7 @@ static void do_unoptimize_kprobes(void)
{
struct optimized_kprobe *op, *tmp;

+ lockdep_assert_held(&text_mutex);
/* See comment in do_optimize_kprobes() */
lockdep_assert_cpus_held();

@@ -520,7 +520,6 @@ static void do_unoptimize_kprobes(void)
if (list_empty(&unoptimizing_list))
return;

- mutex_lock(&text_mutex);
arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
/* Loop free_list for disarming */
list_for_each_entry_safe(op, tmp, &freeing_list, list) {
@@ -537,7 +536,6 @@ static void do_unoptimize_kprobes(void)
} else
list_del_init(&op->list);
}
- mutex_unlock(&text_mutex);
}

/* Reclaim all kprobes on the free_list */
@@ -563,6 +561,7 @@ static void kprobe_optimizer(struct work_struct *work)
{
mutex_lock(&kprobe_mutex);
cpus_read_lock();
+ mutex_lock(&text_mutex);
/* Lock modules while optimizing kprobes */
mutex_lock(&module_mutex);

@@ -590,6 +589,7 @@ static void kprobe_optimizer(struct work_struct *work)
do_free_cleaned_kprobes();

mutex_unlock(&module_mutex);
+ mutex_unlock(&text_mutex);
cpus_read_unlock();
mutex_unlock(&kprobe_mutex);

--
2.20.1
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