Re: 3.14 issue with i810 graphic card bisected

[Tobias Powalowski <tobias.powalowski@googlemail.com>]

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Am 18.04.2014 22:38, schrieb Tejun Heo:
> Hello,
>
> Sorry about the long delay.
>
> On Thu, Apr 03, 2014 at 08:37:49AM +0200, Tobias Powalowski wrote:
>> Hi,
>> I bisected a X startup crash due to new 3.14 kernel:
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/fs/kernfs/file.c?id=9b2db6e1894577d48f4e290381bac6e573593838
>> It's an old intel 810 graphics card which got broken.
>> dmesg and xorg.log attached.
> Hmm... I'm stumped.  The patch shouldn't cause any visible difference
> to the userland.  I went over it a couple more times and still can't
> see how this would make any difference.  Can you please do the
> followings?
>
> * Repeat the test on v3.14 with only the patch reverted.  If it makes
>   the problem go away reliably,
>
> * strace X startup on v3.14 and v3.14 sans the offending patch.
>
> Thanks!
>
Hi,
attached patch which solves my issue with 3.14.1
interesting part are those4 lines:
-    if (ops->mmap)
-        rc = ops->mmap(of, vma);
-    if (rc)
-        goto out_put;
I built kernel with different parts of the bisection patch reverted.
Last I added those reverts and it started working again.

Hope this helps.

greetings
tpowa

-- 
Tobias Powalowski
Archlinux Developer & Package Maintainer (tpowa)
http://www.archlinux.org
tpowa@archlinux.org


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--- linux-3.14/fs/kernfs/file.c.orig	2014-03-31 05:40:15.000000000 +0200
+++ linux-3.14/fs/kernfs/file.c	2014-04-19 08:22:11.754042780 +0200
@@ -458,16 +458,6 @@
 	const struct kernfs_ops *ops;
 	int rc;
 
-	/*
-	 * mmap path and of->mutex are prone to triggering spurious lockdep
-	 * warnings and we don't want to add spurious locking dependency
-	 * between the two.  Check whether mmap is actually implemented
-	 * without grabbing @of->mutex by testing HAS_MMAP flag.  See the
-	 * comment in kernfs_file_open() for more details.
-	 */
-	if (!(of->kn->flags & KERNFS_HAS_MMAP))
-		return -ENODEV;
-
 	mutex_lock(&of->mutex);
 
 	rc = -ENODEV;
@@ -475,7 +468,10 @@
 		goto out_unlock;
 
 	ops = kernfs_ops(of->kn);
+	if (ops->mmap)
+		rc = ops->mmap(of, vma);
+	if (rc)
+		goto out_put;
-	rc = ops->mmap(of, vma);
 
 	/*
 	 * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
--- linux-3.14/fs/sysfs/file.c.old	2014-03-31 05:40:15.000000000 +0200
+++ linux-3.14/fs/sysfs/file.c	2014-04-19 11:18:53.296366182 +0200
@@ -141,7 +141,10 @@
 {
 	struct bin_attribute *battr = of->kn->priv;
 	struct kobject *kobj = of->kn->parent->priv;
-
+	
+	if (!battr->mmap)
+		return -ENODEV;
+	
 	return battr->mmap(of->file, kobj, battr, vma);
 }
 
@@ -194,11 +197,6 @@
 static const struct kernfs_ops sysfs_bin_kfops_rw = {
 	.read		= sysfs_kf_bin_read,
 	.write		= sysfs_kf_bin_write,
-};
-
-static const struct kernfs_ops sysfs_bin_kfops_mmap = {
-	.read		= sysfs_kf_bin_read,
-	.write		= sysfs_kf_bin_write,
 	.mmap		= sysfs_kf_bin_mmap,
 };
 
@@ -234,9 +232,7 @@
 	} else {
 		struct bin_attribute *battr = (void *)attr;
 
-		if (battr->mmap)
-			ops = &sysfs_bin_kfops_mmap;
-		else if (battr->read && battr->write)
+		if ((battr->read && battr->write) || battr->mmap)
 			ops = &sysfs_bin_kfops_rw;
 		else if (battr->read)
 			ops = &sysfs_bin_kfops_ro;

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