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.
Signed-off-by: David Airlie airlied@redhat.com --- drivers/video/console/fbcon.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c index 2e471c2..f8a79fc 100644 --- a/drivers/video/console/fbcon.c +++ b/drivers/video/console/fbcon.c @@ -372,8 +372,12 @@ static void fb_flashcursor(struct work_struct *work) struct vc_data *vc = NULL; int c; int mode; + int ret; + + ret = console_trylock(); + if (ret == 0) + return;
- console_lock(); if (ops && ops->currcon != -1) vc = vc_cons[ops->currcon].d;
So after much tracing with direct netconsole writes (printks under console_lock not so useful), I think I found the race.
Direct netconsole write would be a useful patch to have mainline I think 8)
Hopefully this fixes the problem for anyone seeing vesafb->kms driver handoff.
Not really the proper fix but its clear and is probably the best thing to go in initially with a cc: stable. Can you at least stick a large
+ /* FIXME: we should sort out the unbind locking instead */
on the patch however.
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On Tue, 2012-08-21 at 10:15 +0100, Alan Cox wrote:
So after much tracing with direct netconsole writes (printks under console_lock not so useful), I think I found the race.
Direct netconsole write would be a useful patch to have mainline I think 8)
could we make that use the earlyprintk infrastructure?
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On Tue, Aug 21, 2012 at 7:15 PM, Alan Cox alan@lxorguk.ukuu.org.uk wrote:
So after much tracing with direct netconsole writes (printks under console_lock not so useful), I think I found the race.
Direct netconsole write would be a useful patch to have mainline I think 8)
Well I used a one line wrapper around the netconsole write_msg, which just passed NULL as the first arg, then sprinkled netconsole_write_msg around the place, not having printf stuff could be an annoyance for some people, for this it didn't matter.
Peter I wish I had a serial port to work with :-)
Not really the proper fix but its clear and is probably the best thing to go in initially with a cc: stable. Can you at least stick a large
- /* FIXME: we should sort out the unbind locking instead */
Done, and cc stable, I'll send this to Linus via my tree as its fairly urgent from my pov.
Dave.
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On Tue, 2012-08-21 at 16:40 +1000, Dave Airlie wrote:
So after much tracing with direct netconsole writes (printks under console_lock not so useful)
I always use earlyprintk on serial..
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On Tue, Aug 21, 2012 at 2:40 AM, Dave Airlie airlied@redhat.com wrote:
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.
Signed-off-by: David Airlie airlied@redhat.com
drivers/video/console/fbcon.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c index 2e471c2..f8a79fc 100644 --- a/drivers/video/console/fbcon.c +++ b/drivers/video/console/fbcon.c @@ -372,8 +372,12 @@ static void fb_flashcursor(struct work_struct *work) struct vc_data *vc = NULL; int c; int mode;
int ret;ret = console_trylock();if (ret == 0)return;
console_lock(); if (ops && ops->currcon != -1) vc = vc_cons[ops->currcon].d;
I have a Dell XPS 8300 machine with a Radeon card in it that started showing this problem yesterday with 3.6-rc2 kernels. I tested this patch on top of v3.6-rc2-206-g10c63c9 this morning and the problem seems to have been cleared up for me. That includes making sure the grub2 file has the gfxterm set, etc.
I know we've been seeing this quite a bit more on Fedora 17, so we'll want to have some people test a 3.5 build with it but things are looking better.
josh
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