linux-kernel - 3.13-1 dm cache possible race condition

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Message-ID: <CACiqTEObccUuhyCcr8HZ0qZunxwdtkPLNYsp9xJRG6H6hxGo7Q@mail.gmail.com>
Date:	Sun, 18 May 2014 18:35:46 +0300
From:	roma1390 <roma1390@...il.com>
To:	linux-kernel@...r.kernel.org,
	Morgan Mears <Morgan.Mears@...app.com>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>,
	Joe Thornber <ejt@...hat.com>,
	Heinz Mauelshagen <heinzm@...hat.com>
Subject: 3.13-1 dm cache possible race condition

I think that somehow is got broken cache->nr_dirty

# dmsetup status foo0
0 32768 cache 7/4096 1728240 256 1675650 0 0 64 64 4294967295 1
writeback 2 migration_threshold 2048 4 random_threshold 4
sequential_threshold 512


See: 4294967295 this is -1 as is not OK.


Kernel: Debian stock 3.13-1-amd64

Actions taken:

 modprobe brd
 BLOCKS=$[`blockdev --getsize64 /dev/ram0`/512]
 METADATA_DEV=/dev/ram0
 CACHE_DEV=/dev/ram1
 DATA_DEV=/dev/ram2
 dmsetup create foo0 --table "0 $BLOCKS cache $METADATA_DEV $CACHE_DEV
$DATA_DEV 512 1 writeback default 0"

Test:
one terminal window:
  while true; do dd if=/dev/zero of=/dev/mapper/foo0 bs=512; done
second window:
  while sleep .1; do dmsetup status foo0; done


after some time from 0 i get to 4294967295, which is think is not
expected value.


More info:
device just created:
0 32768 cache 10/4096 1728259 256 1675650 0 0 0 64 0 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
after some (~20) writes:
0 32768 cache 10/4096 1790456 256 1737543 0 0 0 64 0 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
started full speed test, after 2 sec:
0 32768 cache 10/4096 2475934 256 2417479 0 0 0 64 0 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
0 32768 cache 10/4096 2485872 256 2428545 0 0 0 64 5 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
0 32768 cache 10/4096 2495964 256 2437959 0 0 0 64 0 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
0 32768 cache 10/4096 2506447 256 2447365 0 0 0 64 20 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
0 32768 cache 10/4096 2515948 256 2458439 0 0 0 64 0 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
0 32768 cache 10/4096 2526687 256 2466631 0 0 0 64 0 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
after ~10sec:
0 32768 cache 10/4096 2667754 256 2609991 0 0 0 64 0 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
0 32768 cache 10/4096 2678571 256 2618183 0 0 0 64 4294967295 1
writeback 2 migration_threshold 2048 4 random_threshold 4
sequential_threshold 512
0 32768 cache 10/4096 2687846 256 2630471 0 0 0 64 4294967295 1
writeback 2 migration_threshold 2048 4 random_threshold 4
sequential_threshold 512
0 32768 cache 10/4096 2698349 256 2638663 0 0 0 64 4294967295 1
writeback 2 migration_threshold 2048 4 random_threshold 4
sequential_threshold 512
0 32768 cache 10/4096 2708082 256 2648514 0 0 0 64 5 1 writeback 2
migration_threshold 2048 4 random_threshold 4 sequential_threshold 512
0 32768 cache 10/4096 2717700 256 2659143 0 0 0 64 4294967295 1
writeback 2 migration_threshold 2048 4 random_threshold 4
sequential_threshold 512
0 32768 cache 10/4096 2728596 256 2667335 0 0 0 64 4294967295 1
writeback 2 migration_threshold 2048 4 random_threshold 4
sequential_threshold 512
0 32768 cache 10/4096 2737453 256 2679623 0 0 0 64 4294967295 1
writeback 2 migration_threshold 2048 4 random_threshold 4
sequential_threshold 512
^C
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