From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: intel-gfx@lists.freedesktop.org
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, Ben Widawsky <ben@bwidawsk.net>
Subject: [PATCH 2/3] drm/i915: close PM interrupt masking races in the rps work func
Date: Sun, 4 Sep 2011 17:35:01 +0200 [thread overview]
Message-ID: <1315150502-12537-3-git-send-email-daniel.vetter@ffwll.ch> (raw)
In-Reply-To: <1315150502-12537-1-git-send-email-daniel.vetter@ffwll.ch>
This patch closes the following race:
We get a PM interrupt A, mask it, set dev_priv->iir = PM_A and kick of the
work item. Scheduler isn't grumpy, so the work queue takes rps_lock,
grabs pm_iir = dev_priv->pm_iir and pm_imr = READ(PMIMR). Note that
pm_imr == pm_iir because we've just masked the interrupt we've got.
Now hw sends out PM interrupt B (not masked), we process it and mask
it. Later on the irq handler also clears PMIIR.
Then the work item proceeds and at the end clears PMIMR. Because
(local) pm_imr == pm_iir we have
pm_imr & ~pm_iir == 0
so all interrupts are enabled.
Hardware is still interrupt-happy, and sends out a new PM interrupt B.
PMIMR doesn't mask B (it does not mask anything), PMIIR is cleared, so
we get it and hit the WARN in the interrupt handler (because
dev_priv->pm_iir == PM_B).
That's why I've moved the
WRITE(PMIMR, 0)
up under the protection of the rps_lock. And write an uncoditional 0
to PMIMR, because that's what we'll do anyway.
This races looks much more likely because we can arbitrarily extend
the window by grabing dev->struct mutex right after the irq handler
has processed the first PM_B interrupt.
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/i915/i915_irq.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 2fdd9f9..21ebcbd 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -383,6 +383,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
pm_iir = dev_priv->pm_iir;
dev_priv->pm_iir = 0;
pm_imr = I915_READ(GEN6_PMIMR);
+ I915_WRITE(GEN6_PMIMR, 0);
spin_unlock_irq(&dev_priv->rps_lock);
if (!pm_iir)
@@ -420,7 +421,6 @@ static void gen6_pm_rps_work(struct work_struct *work)
* an *extremely* unlikely race with gen6_rps_enable() that is prevented
* by holding struct_mutex for the duration of the write.
*/
- I915_WRITE(GEN6_PMIMR, pm_imr & ~pm_iir);
mutex_unlock(&dev_priv->dev->struct_mutex);
}
--
1.7.6
next prev parent reply other threads:[~2011-09-04 16:34 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-04 3:24 [PATCH] drm/i915: Fix rps irq warning Ben Widawsky
2011-09-04 9:03 ` Chris Wilson
2011-09-04 15:49 ` Ben Widawsky
2011-09-04 15:34 ` [PATCH 0/3] slaughter rps races some more Daniel Vetter
2011-09-04 15:35 ` [PATCH 1/3] drm/i915: close PM interrupt masking races in the irq handler Daniel Vetter
2011-09-04 17:09 ` Ben Widawsky
2011-09-04 15:35 ` Daniel Vetter [this message]
2011-09-04 17:08 ` [PATCH 2/3] drm/i915: close PM interrupt masking races in the rps work func Ben Widawsky
2011-09-04 19:26 ` Daniel Vetter
2011-09-04 19:56 ` Ben Widawsky
2011-09-04 20:10 ` Daniel Vetter
2011-09-04 21:38 ` Ben Widawsky
2011-09-05 6:38 ` Daniel Vetter
2011-09-05 6:51 ` Ben Widawsky
2011-09-05 12:15 ` Chris Wilson
2011-09-04 15:35 ` [PATCH 3/3] drm/i915: close rps work vs. rps disable races Daniel Vetter
2011-09-04 17:23 ` Ben Widawsky
2011-09-04 19:17 ` Daniel Vetter
2011-09-04 19:50 ` Ben Widawsky
2011-09-04 19:57 ` Daniel Vetter
2011-09-05 8:15 ` [PATCH] drm/i915: properly cancel rps_work on module unload Daniel Vetter
2011-09-05 17:27 ` Ben Widawsky
2011-09-08 12:00 [PATCH 1/3] drm/i915: close PM interrupt masking races in the irq handler Daniel Vetter
2011-09-08 12:00 ` [PATCH 2/3] drm/i915: close PM interrupt masking races in the rps work func Daniel Vetter
2011-09-08 15:19 ` Ben Widawsky
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1315150502-12537-3-git-send-email-daniel.vetter@ffwll.ch \
--to=daniel.vetter@ffwll.ch \
--cc=ben@bwidawsk.net \
--cc=intel-gfx@lists.freedesktop.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).