Re: [PATCH 1/3] stop_machine: kill __stop_machine()

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2011-06-14 at 19:06 +0200, Tejun Heo wrote:
> +++ b/arch/x86/kernel/alternative.c
> @@ -719,8 +719,7 @@ void *__kprobes text_poke_smp(void *addr, const void *opcode, size_t len)
>         tpp.nparams = 1;
>         atomic_set(&stop_machine_first, 1);
>         wrote_text = 0;
> -       /* Use __stop_machine() because the caller already got online_cpus. */
> -       __stop_machine(stop_machine_text_poke, (void *)&tpp, cpu_online_mask);
> +       stop_machine(stop_machine_text_poke, (void *)&tpp, cpu_online_mask);
>         return addr;
>  }

Please have a look at: 

---
commit d91309f69b7bdb64aeb30106fde8d18c5dd354b5
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Fri Feb 11 22:07:46 2011 +0100

    x86: Fix text_poke_smp_batch() deadlock
    
    Fix this deadlock - we are already holding the mutex:
    
    =======================================================
    [ INFO: possible circular locking dependency detected ] 2.6.38-rc4-test+ #1
    -------------------------------------------------------
    bash/1850 is trying to acquire lock:
     (text_mutex){+.+.+.}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
    
    but task is already holding lock:
     (smp_alt){+.+...}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
    
    which lock already depends on the new lock.
    
    the existing dependency chain (in reverse order) is:
    
    -> #2 (smp_alt){+.+...}:
           [<ffffffff81082d02>] lock_acquire+0xcd/0xf8
           [<ffffffff8192e119>] __mutex_lock_common+0x4c/0x339
           [<ffffffff8192e4ca>] mutex_lock_nested+0x3e/0x43
           [<ffffffff8101050f>] alternatives_smp_switch+0x77/0x1d8
           [<ffffffff81926a6f>] do_boot_cpu+0xd7/0x762
           [<ffffffff819277dd>] native_cpu_up+0xe6/0x16a
           [<ffffffff81928e28>] _cpu_up+0x9d/0xee
           [<ffffffff81928f4c>] cpu_up+0xd3/0xe7
           [<ffffffff82268d4b>] kernel_init+0xe8/0x20a
           [<ffffffff8100ba24>] kernel_thread_helper+0x4/0x10
    
    -> #1 (cpu_hotplug.lock){+.+.+.}:
           [<ffffffff81082d02>] lock_acquire+0xcd/0xf8
           [<ffffffff8192e119>] __mutex_lock_common+0x4c/0x339
           [<ffffffff8192e4ca>] mutex_lock_nested+0x3e/0x43
           [<ffffffff810568cc>] get_online_cpus+0x41/0x55
           [<ffffffff810a1348>] stop_machine+0x1e/0x3e
           [<ffffffff819314c1>] text_poke_smp_batch+0x3a/0x3c
           [<ffffffff81932b6c>] arch_optimize_kprobes+0x10d/0x11c
           [<ffffffff81933a51>] kprobe_optimizer+0x152/0x222
           [<ffffffff8106bb71>] process_one_work+0x1d3/0x335
           [<ffffffff8106cfae>] worker_thread+0x104/0x1a4
           [<ffffffff810707c4>] kthread+0x9d/0xa5
           [<ffffffff8100ba24>] kernel_thread_helper+0x4/0x10
    
    -> #0 (text_mutex){+.+.+.}:
    
    other info that might help us debug this:
    
    6 locks held by bash/1850:
     #0:  (&buffer->mutex){+.+.+.}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
     #1:  (s_active#75){.+.+.+}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
     #2:  (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
     #3:  (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
     #4:  (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
     #5:  (smp_alt){+.+...}, at: [<ffffffff8100a9c1>] return_to_handler+0x0/0x2f
    
    stack backtrace:
    Pid: 1850, comm: bash Not tainted 2.6.38-rc4-test+ #1
    Call Trace:
    
     [<ffffffff81080eb2>] print_circular_bug+0xa8/0xb7
     [<ffffffff8192e4ca>] mutex_lock_nested+0x3e/0x43
     [<ffffffff81010302>] alternatives_smp_unlock+0x3d/0x93
     [<ffffffff81010630>] alternatives_smp_switch+0x198/0x1d8
     [<ffffffff8102568a>] native_cpu_die+0x65/0x95
     [<ffffffff818cc4ec>] _cpu_down+0x13e/0x202
     [<ffffffff8117a619>] sysfs_write_file+0x108/0x144
     [<ffffffff8111f5a2>] vfs_write+0xac/0xff
     [<ffffffff8111f7a9>] sys_write+0x4a/0x6e
    
    Reported-by: Steven Rostedt <rostedt@goodmis.org>
    Tested-by: Steven Rostedt <rostedt@goodmis.org>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: mathieu.desnoyers@efficios.com
    Cc: rusty@rustcorp.com.au
    Cc: ananth@in.ibm.com
    Cc: masami.hiramatsu.pt@hitachi.com
    Cc: fweisbec@gmail.com
    Cc: jbeulich@novell.com
    Cc: jbaron@redhat.com
    Cc: mhiramat@redhat.com
    LKML-Reference: <1297458466.5226.93.camel@laptop>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 1236085..7038b95 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -671,7 +671,7 @@ void __kprobes text_poke_smp_batch(struct text_poke_param *params, int n)
 
 	atomic_set(&stop_machine_first, 1);
 	wrote_text = 0;
-	stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
+	__stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
 }
 
 #if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL)