lkml.org 
[lkml]   [2021]   [Nov]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.9 168/207] tty: tty_buffer: Fix the softlockup issue in flush_to_ldisc
    Date
    From: Guanghui Feng <guanghuifeng@linux.alibaba.com>

    [ Upstream commit 3968ddcf05fb4b9409cd1859feb06a5b0550a1c1 ]

    When running ltp testcase(ltp/testcases/kernel/pty/pty04.c) with arm64, there is a soft lockup,
    which look like this one:

    Workqueue: events_unbound flush_to_ldisc
    Call trace:
    dump_backtrace+0x0/0x1ec
    show_stack+0x24/0x30
    dump_stack+0xd0/0x128
    panic+0x15c/0x374
    watchdog_timer_fn+0x2b8/0x304
    __run_hrtimer+0x88/0x2c0
    __hrtimer_run_queues+0xa4/0x120
    hrtimer_interrupt+0xfc/0x270
    arch_timer_handler_phys+0x40/0x50
    handle_percpu_devid_irq+0x94/0x220
    __handle_domain_irq+0x88/0xf0
    gic_handle_irq+0x84/0xfc
    el1_irq+0xc8/0x180
    slip_unesc+0x80/0x214 [slip]
    tty_ldisc_receive_buf+0x64/0x80
    tty_port_default_receive_buf+0x50/0x90
    flush_to_ldisc+0xbc/0x110
    process_one_work+0x1d4/0x4b0
    worker_thread+0x180/0x430
    kthread+0x11c/0x120

    In the testcase pty04, The first process call the write syscall to send
    data to the pty master. At the same time, the workqueue will do the
    flush_to_ldisc to pop data in a loop until there is no more data left.
    When the sender and workqueue running in different core, the sender sends
    data fastly in full time which will result in workqueue doing work in loop
    for a long time and occuring softlockup in flush_to_ldisc with kernel
    configured without preempt. So I add need_resched check and cond_resched
    in the flush_to_ldisc loop to avoid it.

    Signed-off-by: Guanghui Feng <guanghuifeng@linux.alibaba.com>
    Link: https://lore.kernel.org/r/1633961304-24759-1-git-send-email-guanghuifeng@linux.alibaba.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/tty/tty_buffer.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
    index ca9c82ee6c35d..dfccc102c1ddd 100644
    --- a/drivers/tty/tty_buffer.c
    +++ b/drivers/tty/tty_buffer.c
    @@ -536,6 +536,9 @@ static void flush_to_ldisc(struct work_struct *work)
    if (!count)
    break;
    head->read += count;
    +
    + if (need_resched())
    + cond_resched();
    }

    mutex_unlock(&buf->lock);
    --
    2.33.0


    \
     
     \ /
      Last update: 2021-11-24 13:30    [W:4.232 / U:0.184 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site