UbiquitousOS
/
OpenCloudOS-Kernel
mirror of https://gitee.com/OpenCloudOS/OpenCloudOS-Kernel.git
11
0
Fork 0
Code Issues Projects Releases Wiki Activity

fbcon: fix race condition between console lock and cursor timer (v1.1) 

So we've had a fair few reports of fbcon handover breakage between
efi/vesafb and i915 surface recently, so I dedicated a couple of
days to finding the problem.

Essentially the last thing we saw was the conflicting framebuffer
message and that was all.

So after much tracing with direct netconsole writes (printks
under console_lock not so useful), I think I found the race.

Thread A (driver load)    Thread B (timer thread)
  unbind_con_driver ->              |
  bind_con_driver ->                |
  vc->vc_sw->con_deinit ->          |
  fbcon_deinit ->                   |
  console_lock()                    |
      |                             |
      |                       fbcon_flashcursor timer fires
      |                       console_lock() <- blocked for A
      |
      |
fbcon_del_cursor_timer ->
  del_timer_sync
  (BOOM)

Of course because all of this is under the console lock,
we never see anything, also since we also just unbound the active
console guess what we never see anything.

Hopefully this fixes the problem for anyone seeing vesafb->kms
driver handoff.

v1.1: add comment suggestion from Alan.

Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Dave Airlie 2012-08-21 16:29:47 +10:00
parent 27fc4f1c0b
commit d8636a2717
1 changed files with 8 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
drivers/video/console/fbcon.c
View File

@ -372,8 +372,15 @@ static void fb_flashcursor(struct work_struct *work)
struct vc_data *vc = NULL;
int c;
int mode;
int ret;
/* FIXME: we should sort out the unbind locking instead */
/* instead we just fail to flash the cursor if we can't get
* the lock instead of blocking fbcon deinit */
ret = console_trylock();
if (ret == 0)
return;
console_lock();
if (ops && ops->currcon != -1)
vc = vc_cons[ops->currcon].d;