[Bug 103525] [CI] igt@* - Incomplete - INFO: task [gem_tiled_swapp|kms_flip] blocked for more than 60 seconds.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103525

--- Comment #4 from Daniel Vetter <daniel at ffwll.ch> ---
I looked at the 2 examples linked, and the common issue seems to be that we're
stuck somewhere in the uart transmit, within printk, which can be called from
anywhere and so block any other task.

So either the serial console can't keep up, or it's broken.

Example backtrace:

<4>[  553.954347] Call Trace:
<4>[  553.954348]  wait_for_xmitr+0x41/0xa0
<4>[  553.954348]  serial8250_console_putchar+0x1c/0x30
<4>[  553.954348]  ? wait_for_xmitr+0xa0/0xa0
<4>[  553.954348]  uart_console_write+0x30/0x70
<4>[  553.954348]  serial8250_console_write+0xd9/0x270
<4>[  553.954349]  ? vt_console_print+0x225/0x3b0
<4>[  553.954349]  ? msg_print_text+0x9d/0x100
<4>[  553.954349]  univ8250_console_write+0x26/0x30
<4>[  553.954349]  console_unlock+0x430/0x570
<4>[  553.954350]  vprintk_emit+0x254/0x3b0
<4>[  553.954350]  ? wake_up_q+0x59/0x80
<4>[  553.954350]  vprintk_default+0x1f/0x30
<4>[  553.954350]  vprintk_func+0x2c/0x90
<4>[  553.954351]  printk+0x43/0x4b

above is the common part that would identify this bug, below can vary depending
upon who's stuck and why:

<4>[  553.954351]  ? drm_helper_hpd_irq_event+0xcc/0x110
<4>[  553.954351]  drm_printk+0x8e/0x90
<4>[  553.954351]  drm_helper_hpd_irq_event+0xcc/0x110
<4>[  553.954352]  i915_hpd_poll_init_work+0xc5/0x100 [i915]
<4>[  553.954352]  process_one_work+0x221/0x650
<4>[  553.954352]  worker_thread+0x4e/0x3c0
<4>[  553.954352]  kthread+0x114/0x150
<4>[  553.954352]  ? process_one_work+0x650/0x650
<4>[  553.954353]  ? kthread_create_on_node+0x40/0x40
<4>[  553.954353]  ret_from_fork+0x27/0x40

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