From f1c6ece23729257fb46562ff9224cf5f61b818da Mon Sep 17 00:00:00 2001 From: Andrea Righi Date: Mon, 12 Aug 2019 20:43:02 +0200 Subject: kprobes: Fix potential deadlock in kprobe_optimizer() 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 Acked-by: Masami Hiramatsu Cc: Anil S Keshavamurthy Cc: David S. Miller Cc: Linus Torvalds Cc: Naveen N. Rao Cc: Peter Zijlstra Cc: Thomas Gleixner 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 --- kernel/kprobes.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'kernel/kprobes.c') diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 9873fc627d61..d9770a5393c8 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -470,6 +470,7 @@ 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. @@ -487,9 +488,7 @@ static void do_optimize_kprobes(void) list_empty(&optimizing_list)) return; - mutex_lock(&text_mutex); arch_optimize_kprobes(&optimizing_list); - mutex_unlock(&text_mutex); } /* @@ -500,6 +499,7 @@ 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(); @@ -507,7 +507,6 @@ 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) { @@ -524,7 +523,6 @@ static void do_unoptimize_kprobes(void) } else list_del_init(&op->list); } - mutex_unlock(&text_mutex); } /* Reclaim all kprobes on the free_list */ @@ -556,6 +554,7 @@ 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); @@ -583,6 +582,7 @@ 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); -- cgit v1.2.3