[GIT,PULL] Cacheflush updates for 3.12

Commit Message

Jon Medhurst (Tixy) Dec. 5, 2013, 9:55 a.m. UTC

On Wed, 2013-12-04 at 16:13 +0000, Will Deacon wrote:
> On Wed, Dec 04, 2013 at 03:37:36PM +0000, Christian Gmeiner wrote:
> > 2013/8/12 Will Deacon <[e-mail]>:
> > > Please pull the following user-cacheflush updates for 3.12. This series both
> > > improves performance of cacheflush-heavy workloads (i.e. browser benchmarks)
> > > and also addresses a DoS issue on non-preemptible systems.
> 
> [...]
> 
> > Hi all.
> 
> Hello,
> 
> > I spend the last day running a bisect and I think I have found a problem :)
> > 
> > I have a simple automated test case running, which looks like this:
> > 
> > imx6d based device running X, chromium and x11vnc <----> windows pc connected
> > via VNC to the device. With this patchset applyed the browser tab
> > crashed after about
> > 5 minutes hitting the F5/refresh button every 1-3 seconds.
> 
> Hmm... it would be great if we had a simpler way to reproduce this, but ok.
> How many cores do you have on your IMX6? Also, how does the browser tab crash?
> Does it receive a SIGILL?

I think I'm also seeing this problem with Linaro Android on vexpress.
The latest Android version (KitKat) has moved to using the Chrome
browser and it crashes very easily after just a few seconds use (with
SIGSEGV's because execution jumped into kernel virtual memory range).

The reason I think it's the same issue as talked about in this email is
that after reading this I check a 3.10 kernel with the same Android
image and that was fine. Then I tried a previously crashing 3.13-rc2
kernel with the hack below to undo $subject, and that stopped the
crashes:

A Linaro Android vexpress build which shows the bug can de found at
https://android-build.linaro.org/builds/~linaro-android/vexpress-linaro/#build=172

And the bug is being tracked at 
https://bugs.launchpad.net/linaro-android/+bug/1254750
(ignore comments on that report about serial console issues, they should
have been on a different bug report)

Patch

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index dbf0923..ff58932 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -560,7 +560,7 @@  do_cache_op(unsigned long start, unsigned long end,
int flags)
        if (!access_ok(VERIFY_READ, start, end - start))
                return -EFAULT;
 
-       return __do_cache_op(start, end);
+       return flush_cache_user_range(start, end);
 }