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


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