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drm/fb-helper: Don't schedule_work() to flush frame buffer during panic()

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[ Upstream commit 833cd3e9ad ]

Sometimes the system [1] hangs on x86 I/O machine checks. However, the
expected behavior is to reboot the system, as the machine check handler
ultimately triggers a panic(), initiating a reboot in the last step.

The root cause is that sometimes the panic() is blocked when
drm_fb_helper_damage() invoking schedule_work() to flush the frame buffer.
This occurs during the process of flushing all messages to the frame
buffer driver as shown in the following call trace:

  Machine check occurs [2]:
    panic()
      console_flush_on_panic()
        console_flush_all()
          console_emit_next_record()
            con->write()
              vt_console_print()
                hide_cursor()
                  vc->vc_sw->con_cursor()
                    fbcon_cursor()
                      ops->cursor()
                        bit_cursor()
                          soft_cursor()
                            info->fbops->fb_imageblit()
                              drm_fbdev_generic_defio_imageblit()
                                drm_fb_helper_damage_area()
                                  drm_fb_helper_damage()
                                    schedule_work() // <--- blocked here
    ...
    emergency_restart()  // wasn't invoked, so no reboot.

During panic(), except the panic CPU, all the other CPUs are stopped.
In schedule_work(), the panic CPU requires the lock of worker_pool to
queue the work on that pool, while the lock may have been token by some
other stopped CPU. So schedule_work() is blocked.

Additionally, during a panic(), since there is no opportunity to execute
any scheduled work, it's safe to fix this issue by skipping schedule_work()
on 'oops_in_progress' in drm_fb_helper_damage().

[1] Enable the kernel option CONFIG_FRAMEBUFFER_CONSOLE,
    CONFIG_DRM_FBDEV_EMULATION, and boot with the 'console=tty0'
    kernel command line parameter.

[2] Set 'panic_timeout' to a non-zero value before calling panic().

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reported-by: Yudong Wang <yudong.wang@intel.com>
Tested-by: Yudong Wang <yudong.wang@intel.com>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240703141737.75378-1-qiuxu.zhuo@intel.com
Signed-off-by: Maarten Lankhorst,,, <maarten.lankhorst@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Qiuxu Zhuo 2024-07-03 22:17:37 +08:00 committed by Greg Kroah-Hartman
parent df1a7cc5e0
commit d5618eaea8
1 changed files with 11 additions and 0 deletions
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11
drivers/gpu/drm/drm_fb_helper.c
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@ -631,6 +631,17 @@ static void drm_fb_helper_add_damage_clip(struct drm_fb_helper *helper, u32 x, u
static void drm_fb_helper_damage(struct drm_fb_helper *helper, u32 x, u32 y,
u32 width, u32 height)
{
/*
* This function may be invoked by panic() to flush the frame
* buffer, where all CPUs except the panic CPU are stopped.
* During the following schedule_work(), the panic CPU needs
* the worker_pool lock, which might be held by a stopped CPU,
* causing schedule_work() and panic() to block. Return early on
* oops_in_progress to prevent this blocking.
*/
if (oops_in_progress)
return;
drm_fb_helper_add_damage_clip(helper, x, y, width, height);
schedule_work(&helper->damage_work);