by 平松雅巳 / HIRAMATU，MASAMI

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Subject: Re: [tip:perf/core] x86: Introduce text_poke_smp_batch() for batch-code modifying

(2011/02/12 6:07), Peter Zijlstra wrote:
> On Mon, 2010-12-06 at 18:17 +0000, tip-bot for Masami Hiramatsu wrote:
>
>> @@ -631,10 +639,13 @@ static int __kprobes stop_machine_text_poke(void *data)
>> void *__kprobes text_poke_smp(void *addr, const void *opcode, size_t len)
>> {
>> struct text_poke_params tpp;
>> + struct text_poke_param p;
>>
>> - tpp.addr = addr;
>> - tpp.opcode = opcode;
>> - tpp.len = len;
>> + p.addr = addr;
>> + p.opcode = opcode;
>> + p.len = len;
>> + tpp.params = &p;
>> + tpp.nparams = 1;
>> atomic_set(&stop_machine_first, 1);
>> wrote_text = 0;
>> /* Use __stop_machine() because the caller already got online_cpus. */
>
> ^^^^^^^^^
>
>> @@ -642,6 +653,26 @@ void *__kprobes text_poke_smp(void *addr, const void *opcode, size_t len)
>> return addr;
>> }
>>
>> +/**
>> + * text_poke_smp_batch - Update instructions on a live kernel on SMP
>> + * @params: an array of text_poke parameters
>> + * @n: the number of elements in params.
>> + *
>> + * Modify multi-byte instruction by using stop_machine() on SMP. Since the
>> + * stop_machine() is heavy task, it is better to aggregate text_poke requests
>> + * and do it once if possible.
>> + *
>> + * Note: Must be called under get_online_cpus() and text_mutex.
>> + */
>> +void __kprobes text_poke_smp_batch(struct text_poke_param *params, int n)
>> +{
>> + struct text_poke_params tpp = {.params = params, .nparams = n};
>> +
>> + atomic_set(&stop_machine_first, 1);
>> + wrote_text = 0;
>> + stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
>> +}
>
> ^^^^^^^^^^^^^^

Oops! Indeed, it's my mistake.
Thank you for reporting & fixing!

>
>
> ---
> Subject: x86: Fix text_poke_smp_batch() deadlock
>
> =======================================================
> [ 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 <[email protected]>
> Tested-by: Steven Rostedt <[email protected]>
> Signed-off-by: Peter Zijlstra <[email protected]>

Acked-by: Masami Hiramatsu <[email protected]>

> ---
> arch/x86/kernel/alternative.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> 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)
>
--
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: [email protected]