On Monday 10 September 2012 10:49:05 Tomi Valkeinen wrote:
> On Sat, 2012-09-08 at 18:05 +0300, Dimitar Dimitrov wrote:
> > Very rare kernel crashes are reported on a custom OMAP4 board. Kernel
> > panics due to corrupted completion structure while executing
> >
> > dispc_irq_wait_handler(). Excerpt from kernel log:
> > Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP
> > Unable to handle kernel paging request at virtual address 00400130
> > ...
> > PC is at 0xebf205bc
> > LR is at __wake_up_common+0x54/0x94
> > ...
> > (__wake_up_common+0x0/0x94)
> > (complete+0x0/0x60)
> > (dispc_irq_wait_handler.36902+0x0/0x14)
> > (omap_dispc_irq_handler+0x0/0x354)
> > (handle_irq_event_percpu+0x0/0x188)
> > (handle_irq_event+0x0/0x64)
> > (handle_fasteoi_irq+0x0/0x10c)
> > (generic_handle_irq+0x0/0x48)
> > (asm_do_IRQ+0x0/0xc0)
> >
> > DISPC IRQ executes callbacks with dispc.irq_lock released. Hence
> > unregister_isr() and DISPC IRQ might be running in parallel on different
> > CPUs. So there is a chance that a callback is executed even though it
> > has been unregistered. As omap_dispc_wait_for_irq_timeout() declares a
> > completion on stack, the dispc_irq_wait_handler() callback might try to
> > access a completion structure that is invalid. This leads to crashes and
> > hangs.
> >
> > Solution is to divide unregister calls into two sets:
> > 1. Non-strict unregistering of callbacks. Callbacks could safely be
> >
> > executed after unregistering them. This is the case with unregister
> > calls from the IRQ handler itself.
> >
> > 2. Strict (synchronized) unregistering. Callbacks are not allowed
> >
> > after unregistering. This is the case with completion waiting.
> >
> > The above solution should satisfy one of the original intentions of the
> > driver: callbacks should be able to unregister themselves.
> >
> > Also fix DSI IRQ unregister which has similar logic to DISPC IRQ
> > handling.
> >
> > Signed-off-by: Dimitar Dimitrov <dinuxbg@xxxxxxxxx>
> > ---
> >
> > WARNING: This bug is quite old. The patch has been tested on v3.0. No
> > testing has been done after rebasing to v3.6. Hence the RFC tag.
> > Hopefully someone will beat me in testing with latest linux-omap/master.
> >
> > Changes since v1 per Tomi Valkeinen's comments:
> > - Don't rename omap_dispc_unregister_isr, just introduce nosync
> > variant. - Apply the same fix for DSI IRQ which suffers from the same
> > race condition.
>
> I made a quick test and works for me, although I haven't encountered the
> problem itself.
This issue is very rarely seen during normal operation. You may not hit it
even after days of stress testing. To speed up reproducing an artificial delay
in the IRQ routine could be used while stress-testing DSS, e.g.:
@@ -3462,6 +3462,8 @@ static irqreturn_t omap_dispc_irq_handler(int irq, void
*a
spin_unlock(&dispc.irq_lock);
+ { static int iii; if ((iii++ % 10) == 0) mdelay(100); }
+
for (i = 0; i < DISPC_MAX_NR_ISRS; i++) {
isr_data = ®istered_isr[i];
>
> Some mostly cosmetic comments below.
>
> This seems to apply cleanly to v3.4+ kernels, but not earlier ones. Do
> you want to make the needed modifications and mail this and the modified
> patches for stable kernels also? I can do that also if you don't want
> to.
I can do the rebase and cleanup. I'll send the modified patch per your
comments in the next hour.
Currently I cannot test, though. I hope to have a working setup by end of week
in order to send sanity-tested patches for stable kernels.
>
> > drivers/staging/omapdrm/omap_plane.c | 2 +-
> > drivers/video/omap2/dss/apply.c | 2 +-
> > drivers/video/omap2/dss/dispc.c | 45
> > +++++++++++++++++++++++++++++----- drivers/video/omap2/dss/dsi.c
> > | 19 ++++++++++++++
> > include/video/omapdss.h | 1 +
> > 5 files changed, 61 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/staging/omapdrm/omap_plane.c
> > b/drivers/staging/omapdrm/omap_plane.c index 7997be7..8d8aa5b 100644
> > --- a/drivers/staging/omapdrm/omap_plane.c
> > +++ b/drivers/staging/omapdrm/omap_plane.c
> > @@ -82,7 +82,7 @@ static void dispc_isr(void *arg, uint32_t mask)
> >
> > struct omap_plane *omap_plane = to_omap_plane(plane);
> > struct omap_drm_private *priv = plane->dev->dev_private;
> >
> > - omap_dispc_unregister_isr(dispc_isr, plane,
> > + omap_dispc_unregister_isr_nosync(dispc_isr, plane,
> >
> > id2irq[omap_plane->ovl->id]);
> >
> > queue_work(priv->wq, &omap_plane->work);
> >
> > diff --git a/drivers/video/omap2/dss/apply.c
> > b/drivers/video/omap2/dss/apply.c index 0fefc68..9386834 100644
> > --- a/drivers/video/omap2/dss/apply.c
> > +++ b/drivers/video/omap2/dss/apply.c
> > @@ -847,7 +847,7 @@ static void dss_unregister_vsync_isr(void)
> >
> > for (i = 0; i < num_mgrs; ++i)
> >
> > mask |= dispc_mgr_get_framedone_irq(i);
> >
> > - r = omap_dispc_unregister_isr(dss_apply_irq_handler, NULL, mask);
> > + r = omap_dispc_unregister_isr_nosync(dss_apply_irq_handler, NULL,
> > mask);
> >
> > WARN_ON(r);
> >
> > dss_data.irq_enabled = false;
> >
> > diff --git a/drivers/video/omap2/dss/dispc.c
> > b/drivers/video/omap2/dss/dispc.c index ee9e296..a67d92c 100644
> > --- a/drivers/video/omap2/dss/dispc.c
> > +++ b/drivers/video/omap2/dss/dispc.c
> > @@ -2421,8 +2421,8 @@ static void dispc_mgr_enable_digit_out(bool enable)
> >
> > enable ? "start" : "stop");
> >
> > }
> >
> > - r = omap_dispc_unregister_isr(dispc_disable_isr,
> > &frame_done_completion, - irq_mask);
> > + r = omap_dispc_unregister_isr(dispc_disable_isr,
> > + &frame_done_completion, irq_mask);
>
> This change is not needed.
Sorry, I missed those. Will remove and resend.
>
> > if (r)
> >
> > DSSERR("failed to unregister %x isr\n", irq_mask);
> >
> > @@ -3320,7 +3320,8 @@ err:
> > }
> > EXPORT_SYMBOL(omap_dispc_register_isr);
> >
> > -int omap_dispc_unregister_isr(omap_dispc_isr_t isr, void *arg, u32 mask)
> > +/* WARNING: callback might be executed even after this function returns!
> > */ +int omap_dispc_unregister_isr_nosync(omap_dispc_isr_t isr, void
> > *arg, u32 mask)
> >
> > {
> >
> > int i;
> > unsigned long flags;
> >
> > @@ -3352,7 +3353,37 @@ int omap_dispc_unregister_isr(omap_dispc_isr_t
> > isr, void *arg, u32 mask)
> >
> > return ret;
> >
> > }
> >
> > -EXPORT_SYMBOL(omap_dispc_unregister_isr);
> > +EXPORT_SYMBOL(omap_dispc_unregister_isr_nosync);
> > +
> > +/*
> > + * Ensure that callback <isr> will NOT be executed after this function
> > + * returns. Must be called from sleepable context, though!
> > + */
> > +int omap_dispc_unregister_isr(omap_dispc_isr_t isr, void *arg, u32 mask)
> > +{
> > + int ret;
> > +
> > + ret = omap_dispc_unregister_isr_nosync(isr, arg, mask);
> > +
> > + /* Task context is not really needed. But if we're called from atomic
> > + * context, it is probably from DISPC IRQ, where we will deadlock.
> > + * So use might_sleep() to catch potential deadlocks.
> > + */
>
> Use the kernel multi-line comment style, i.e.:
>
> /*
> * foobar
> */
Will fix.
>
> > + might_sleep();
> > +
> > +#if defined(CONFIG_SMP)
> > + /* DISPC IRQ executes callbacks with dispc.irq_lock released. Hence
> > + * unregister_isr() and DISPC IRQ might be running in parallel on
> > + * different CPUs. So there is a chance that a callback is executed
> > + * even though it has been unregistered. Add a barrier, in order to
> > + * ensure that after returning from this function, the new DISPC IRQ
> > + * will use an updated callback array, and NOT its cached copy.
> > + */
>
> Comment style here also.
Will fix.
>
> > + synchronize_irq(dispc.irq);
> > +#endif
>
> Why do you use #if defined(CONFIG_SMP)? synchronize_irq is defined
> with !CONFIG_SMP also. In that case it becomes just barrier().
>
You're correct. I'll remove "defined(CONFIG_SMP)".
> > +
> > + return ret;
> > +}
I forgot to keep EXPORT_SYMBOL for omap_dispc_unregister_isr. Will add it.
> >
> > #ifdef DEBUG
> > static void print_irq_status(u32 status)
> >
> > @@ -3567,7 +3598,8 @@ int omap_dispc_wait_for_irq_timeout(u32 irqmask,
> > unsigned long timeout)
> >
> > timeout = wait_for_completion_timeout(&completion, timeout);
> >
> > - omap_dispc_unregister_isr(dispc_irq_wait_handler, &completion,
> > irqmask); + omap_dispc_unregister_isr(dispc_irq_wait_handler,
> > &completion, + irqmask);
>
> Change not needed.
Will remove.
>
> > if (timeout == 0)
> >
> > return -ETIMEDOUT;
> >
> > @@ -3598,7 +3630,8 @@ int
> > omap_dispc_wait_for_irq_interruptible_timeout(u32 irqmask,
> >
> > timeout = wait_for_completion_interruptible_timeout(&completion,
> >
> > timeout);
> >
> > - omap_dispc_unregister_isr(dispc_irq_wait_handler, &completion,
> > irqmask); + omap_dispc_unregister_isr(dispc_irq_wait_handler,
> > &completion, + irqmask);
>
> Change not needed.
Will remove.
>
> > if (timeout == 0)
> >
> > return -ETIMEDOUT;
> >
> > diff --git a/drivers/video/omap2/dss/dsi.c
> > b/drivers/video/omap2/dss/dsi.c index b07e886..24b4a3e 100644
> > --- a/drivers/video/omap2/dss/dsi.c
> > +++ b/drivers/video/omap2/dss/dsi.c
> > @@ -960,6 +960,13 @@ static int dsi_unregister_isr(struct platform_device
> > *dsidev,
> >
> > spin_unlock_irqrestore(&dsi->irq_lock, flags);
> >
> > + might_sleep();
> > +
> > +#if defined(CONFIG_SMP)
> > + /* See notes for dispc.c:omap_dispc_unregister_isr() . */
> > + synchronize_irq(dsi->irq);
> > +#endif
> > +
>
> Same SMP comment as with dispc.
>
> Tomi
Thanks,
Dimitar
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