Strange Hammer test; Problem or Bug ?

[Mancooo]

Hi,

I have a strange problem with testing my ram. I have the following ram (8 Gb in total):

2 x 4GB DDR3 XMP PC3-12800 / BLT4G3D1608ET3LX0 8-8-8-24 / 800 MHz / 1.500V

And the following CPU:

Core i3-4330

The ram can run @1600 Mhz or @1333 Mhz.

I have run allot of tests with this ram (all tests are run with both sticks installed on the motherboard, Asus H96M-Plus). All tests run fine with no errors. I only get the warning during the Hammer test about the High Frequency Row Hammer Bit Flips.

The funny thing is that the warning does not occur when I just do the Hammer test (without the other tests) when the ram is @1333 Mhz. The warning does occur when I do all the tests @1333 Mhz.

When the ram is @1600 Mhz the warning always occurs, either running just the Hammer test or all the tests.

The following warning (always at the exact same spot!) is issued:

2015-11-30 17:28:32 - [MEM WARNING] Test: 13, CPU: 0, Address: 21A586DA8, Expected: 00000000, Actual: 00000400 
2015-11-30 17:28:33 - Fast hammering test failed. Repeat test again with slow hammering. Slow hammering shall performed for the remainder of the test. 
2015-11-30 17:28:34 - RunHammerTest - Running hammer test on 4 CPUs (127MB each) 
2015-11-30 17:28:57 - Slow hammering test passed. Warnings reported

2015-11-30 18:02:34 - [MEM WARNING] Test: 13, CPU: 0, Address: 21A586DA8, Expected: 00000000, Actual: 00000400 
2015-11-30 18:02:35 - Fast hammering test failed. Repeat test again with slow hammering. Slow hammering shall performed for the remainder of the test. 
2015-11-30 18:02:36 - RunHammerTest - Running hammer test on 4 CPUs (127MB each) 
2015-11-30 18:02:59 - Slow hammering test passed. Warnings reported

2015-11-30 18:41:44 - [MEM WARNING] Test: 13, CPU: 0, Address: 21A586DA8, Expected: 00000000, Actual: 00000400 
2015-11-30 18:41:44 - Fast hammering test failed. Repeat test again with slow hammering. Slow hammering shall performed for the remainder of the test. 
2015-11-30 18:41:46 - RunHammerTest - Running hammer test on 4 CPUs (127MB each) 
2015-11-30 18:42:09 - Slow hammering test passed. Warnings reported

Besides the above, I have also tested my ram with the Google Rowhammer-test (https://github.com/google/rowhammer-test). I have run the test for about an hour and no errors or warnings were issued.

So my question is, is my ram faulty (the ram is not older than six months) or is it some kind of bug?

Edit: I just noticed the warning always occurs exactly at the middle of the RunHammerTest, this is the complete log of just the Hammer test;

2015-11-30 17:58:16 - Start hammer test (0x0 - 0x21FE00000) 
2015-11-30 17:58:16 - Locking all memory ranges first... 
2015-11-30 17:58:17 - Memory range locked: 0x1000 - 0x58000 (7636400KB of available memory left) 
2015-11-30 17:58:18 - Memory range locked: 0x59000 - 0x90000 (7636180KB of available memory left) 
2015-11-30 17:58:19 - Memory range locked: 0x91000 - 0x9E000 (7636128KB of available memory left) 
2015-11-30 17:58:19 - Memory range locked: 0x100000 - 0xA1B6A000 (4987640KB of available memory left) 
2015-11-30 17:58:20 - Memory range locked: 0xA1C6A000 - 0xA4E86000 (4936328KB of available memory left) 
2015-11-30 17:58:21 - Memory range locked: 0xA5B69000 - 0xB2BA4000 (4723100KB of available memory left) 
2015-11-30 17:58:22 - Memory range locked: 0xB330A000 - 0xB3885000 (4717488KB of available memory left) 
2015-11-30 17:58:23 - Memory range locked: 0xB38D8000 - 0xB3904000 (4717312KB of available memory left) 
2015-11-30 17:58:23 - Memory range locked: 0xB391C000 - 0xB3934000 (4717216KB of available memory left) 
2015-11-30 17:58:24 - Memory range locked: 0xB393E000 - 0xB3945000 (4717188KB of available memory left) 
2015-11-30 17:58:25 - Memory range locked: 0xB395A000 - 0xB395B000 (4717184KB of available memory left) 
2015-11-30 17:58:26 - Memory range locked: 0xBC27B000 - 0xBC31B000 (4716544KB of available memory left) 
2015-11-30 17:58:26 - Reducing memory range: 0x100000000 - 0x21FE00000 ==> 0x100000000 - 0x21FD00000 
2015-11-30 17:58:27 - Memory range locked: 0x100000000 - 0x21FD00000 (1024KB of available memory left) 
2015-11-30 17:58:28 - All memory ranges successfully locked 
2015-11-30 17:58:35 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 17:58:52 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 17:59:08 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 17:59:24 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 17:59:40 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:00:03 - RunHammerTest - Running hammer test on 4 CPUs (52MB each) 
2015-11-30 18:00:19 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:00:35 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:00:51 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:01:07 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:01:23 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:01:40 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:01:56 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:02:12 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:02:28 - RunHammerTest - Running hammer test on 4 CPUs (127MB each) 
2015-11-30 18:02:34 - [MEM WARNING] Test: 13, CPU: 0, Address: 21A586DA8, Expected: 00000000, Actual: 00000400 
2015-11-30 18:02:35 - Fast hammering test failed. Repeat test again with slow hammering. Slow hammering shall performed for the remainder of the test. 
2015-11-30 18:02:36 - RunHammerTest - Running hammer test on 4 CPUs (127MB each) 
2015-11-30 18:02:59 - Slow hammering test passed. Warnings reported 
2015-11-30 18:03:06 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:03:30 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:03:54 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:04:17 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:04:41 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:05:21 - RunHammerTest - Running hammer test on 4 CPUs (52MB each) 
2015-11-30 18:05:46 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:06:09 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:06:33 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:06:57 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:07:20 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:07:44 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:08:08 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:08:32 - RunHammerTest - Running hammer test on 4 CPUs (128MB each) 
2015-11-30 18:08:55 - RunHammerTest - Running hammer test on 4 CPUs (127MB each) 
2015-11-30 18:09:18 - Cleanup - Unlocking all memory ranges...

[David (PassMark)]

Expected: 00000000, Actual: 00000400

This type of 1 bit difference is exactly what is expected from a row hammer error. So I think it is a real bit flip and not a bug in the software.

Maybe it is slightly random or temperature dependant. So running other tests prior warms up the RAM sticks slightly, making an error more likely.

[Mancooo]

David,

Thanks for your reply!

But is it not odd that the warning always is at the same memory address and always at the middle of the hammer test?

If it really is a bit flip, that is some predictable bit flip

IMO (and I don't know much about how ram works), this has to do with the two sticks of ram being used at the same time. I think that if I test the sticks individually there will be no warning. When I have some more time, I will test that also.

My main concern right now is if I should ask for new ram. Because the system it runs in, is very important to me. And I don't want to have stability or security issues (not that I have any issues right now). Do you recommend getting a new pair of ram?