On Mon, May 25, 2015 at 01:05:15PM +0300, Kirill A. Shutemov wrote:

On Sun, May 24, 2015 at 09:34:04PM +0200, Christoffer Dall wrote:

quoted

Hi all,

I noticed a regression on my arm64 APM X-Gene system a couple
of weeks back.  I would occassionally see the system lock up and see RCU
stalls during the caching phase of kernbench.  I then wrote a small
script that does nothing but cache the files
(http://paste.ubuntu.com/11324767/) and ran that in a loop.  On a known
bad commit (v4.1-rc2), out of 25 boots, I never saw it get past 21
iterations of the loop.  I have since tried to run a bisect from v3.19 to
v4.0 using 100 iterations as my criteria for a good commit.

This resulted in the following first bad commit:

10359213d05acf804558bda7cc9b8422a828d1cd
(mm: incorporate read-only pages into transparent huge pages, 2015-02-11)

Indeed, running the workload on v4.1-rc4 still produced the behavior,
but reverting the above commit gets me through 100 iterations of the
loop.

I have not tried to reproduce on an x86 system.  Turning on a bunch
of kernel debugging features *seems* to hide the problem.  My config for
the XGene system is defconfig + CONFIG_BRIDGE and
CONFIG_POWER_RESET_XGENE.

Please let me know if I can help test patches or other things I can
do to help.  I'm afraid that by simply reading the patch I didn't see
anything obviously wrong with it which would cause this behavior.

I don't see the problem on x86.

I'm wondering if we could have some weird combination of how the
specific architecture works along with these patches...

Some backtraces could help to track it down.

I don't really get backtraces as the sytem just locks up.  But here are
some of the RCU stalls as I've observed them on the console:

http://paste.ubuntu.com/11014701/
http://paste.ubuntu.com/11023143/
http://paste.ubuntu.com/11023261/


Occasionally, I also get this error from the SATA system at the moment
when I power off the device, but not sure if it is related:

  ata1: exception Emask 0x10 SAct 0x0 SErr 0x180000 action 0xe frozen
  ata1: irq_stat 0x00400000, PHY RDY changed
  ata1: SError: { 10B8B Dispar }

Thanks,
-Christoffer