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    Subject[RFC] [PATCH -rt 3/5] printk: don't call printk_tick in printk_needs_cpu()
    Date
    printk_tick() can't be called in atomic context, otherwise below
    warning will show:

    [ 117.597095] BUG: sleeping function called from invalid context at kernel/rtmutex.c:645
    [ 117.597102] in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: kworker/0:0
    [ 117.597111] Pid: 0, comm: kworker/0:0 Not tainted 3.0.6-rt17-00284-gb76d419-dirty #7
    [ 117.597116] Call Trace:
    [ 117.597131] [<c06e3b61>] ? printk+0x1d/0x24
    [ 117.597142] [<c01390b6>] __might_sleep+0xe6/0x110
    [ 117.597151] [<c06e634c>] rt_spin_lock+0x1c/0x30
    [ 117.597158] [<c0142f26>] __wake_up+0x26/0x60
    [ 117.597166] [<c014c78e>] printk_tick+0x3e/0x40
    [ 117.597173] [<c014c7b4>] printk_needs_cpu+0x24/0x30
    [ 117.597181] [<c017ecc8>] tick_nohz_stop_sched_tick+0x2e8/0x410
    [ 117.597191] [<c017305a>] ? sched_clock_idle_wakeup_event+0x1a/0x20
    [ 117.597201] [<c010182a>] cpu_idle+0x4a/0xb0
    [ 117.597209] [<c06e0b97>] start_secondary+0xd3/0xd7

    Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
    ---
    kernel/printk.c | 4 ++--
    1 files changed, 2 insertions(+), 2 deletions(-)

    diff --git a/kernel/printk.c b/kernel/printk.c
    index 0c9a0ab..a50af4e 100644
    --- a/kernel/printk.c
    +++ b/kernel/printk.c
    @@ -1282,8 +1282,8 @@ void printk_tick(void)

    int printk_needs_cpu(int cpu)
    {
    - if (cpu_is_offline(cpu))
    - printk_tick();
    + if (unlikely(cpu_is_offline(cpu)))
    + __this_cpu_write(printk_pending, 0);
    return __this_cpu_read(printk_pending);
    }

    --
    1.7.1


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