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Re: [Xen-devel] Creating a vm with a non-existent /dev/mapper/ tap2 device effectively hangs dom0 system

  • To: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Nathan March <nathan@xxxxxx>
  • Date: Thu, 28 Jul 2011 12:00:53 -0700
  • Delivery-date: Thu, 28 Jul 2011 12:05:15 -0700
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On 7/27/2011 4:29 PM, Nathan March wrote:
Have an interesting one here, originally found on xen 4.1.0 but just upgraded to xen 4.1.1 and it's still here.
Creating a VM with a tap2 device pointed at /dev/mapper/something, when that device doesn't exist, causes the tapdisk2 process to go into D mode and also manages to take out any process that queries it.
This also happens on proper shutdown of a VM, so I must have done something crazy to the setup here since other people haven't been complaining. If I start a VM, strace it's tapdisk2 and then send the VM a shutdown, the strace shows tapdisk2 hanging here: 

12037 gettimeofday({1311879426, 739622}, NULL) = 0
12037 gettimeofday({1311879426, 739717}, NULL) = 0
12037 select(8, [3 4 7], [], [], {600, 0}) = 1 (in [3], left {599, 993029})
12037 gettimeofday({1311879426, 746896}, NULL) = 0
12037 accept(3, 0, NULL)                = 6
12037 gettimeofday({1311879426, 747079}, NULL) = 0
12037 gettimeofday({1311879426, 747169}, NULL) = 0
12037 gettimeofday({1311879426, 747257}, NULL) = 0
12037 select(8, [3 4 6 7], [], [], {600, 0}) = 1 (in [6], left {599, 999948}) 
12037 gettimeofday({1311879426, 747544}, NULL) = 0
12037 select(7, [6], NULL, NULL, {2, 0}) = 1 (in [6], left {1, 999998})
12037 read(6, "\r\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 280) = 280 
12037 gettimeofday({1311879426, 747932}, NULL) = 0
12037 sendto(5, "<30>Jul 28 11:57:06 tapdisk2[12036]: received 'close' message (uuid = 0)\n", 73, MSG_NOSIGNAL, NULL, 0) = 73 
12037 close(8)                          = 0
12037 gettimeofday({1311879426, 749118}, NULL) = 0
12037 sendto(5, "<30>Jul 28 11:57:06 tapdisk2[12036]: closed image /dev/mapper/nathanxenuk1 (0 users, state: 0x00000000, type: 0)\n", 113, MSG_NOSIGNAL, NULL, 0) = 113 
12037 gettimeofday({1311879426, 749536}, NULL) = 0
12037 sendto(5, "<30>Jul 28 11:57:06 tapdisk2[12036]: sending 'close response' message (uuid = 0)\n", 81, MSG_NOSIGNAL, NULL, 0) = 81 
12037 select(7, NULL, [6], NULL, {2, 0}) = 1 (out [6], left {1, 999998})
12037 write(6, "\16\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 280) = 280 
12037 close(6)                          = 0
12037 gettimeofday({1311879426, 750295}, NULL) = 0
12037 gettimeofday({1311879426, 750384}, NULL) = 0
12037 select(8, [3 4 7], [], [], {600, 0}) = 1 (in [3], left {599, 999936})
12037 gettimeofday({1311879426, 750690}, NULL) = 0
12037 accept(3, 0, NULL)                = 6
12037 gettimeofday({1311879426, 750801}, NULL) = 0
12037 gettimeofday({1311879426, 750854}, NULL) = 0
12037 gettimeofday({1311879426, 750905}, NULL) = 0
12037 select(8, [3 4 6 7], [], [], {600, 0}) = 1 (in [6], left {599, 999946}) 
12037 gettimeofday({1311879426, 751085}, NULL) = 0
12037 select(7, [6], NULL, NULL, {2, 0}) = 1 (in [6], left {1, 999998})
12037 read(6, "\17\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 280) = 280 
12037 gettimeofday({1311879426, 751550}, NULL) = 0
12037 sendto(5, "<30>Jul 28 11:57:06 tapdisk2[12036]: received 'detach' message (uuid = 0)\n", 74, MSG_NOSIGNAL, NULL, 0) = 74 
12037 close(7)                          = 0
12037 munmap(0x7ffc389d7000, 1445888

COMMAND    PID USER   FD   TYPE             DEVICE SIZE/OFF   NODE NAME
tapdisk2 12037 root  cwd    DIR                8,1     4096      2 /
tapdisk2 12037 root  rtd    DIR                8,1     4096      2 /
tapdisk2 12037 root txt REG 8,1 496268 180124 /usr/sbin/tapdisk2 tapdisk2 12037 root mem REG 8,1 1412272 268124 /lib64/libc-2.11.2.so tapdisk2 12037 root mem REG 8,1 534648 267759 /lib64/libm-2.11.2.so tapdisk2 12037 root mem REG 8,1 137732 267539 /lib64/libpthread-2.11.2.so tapdisk2 12037 root mem REG 8,1 14512 267757 /lib64/libdl-2.11.2.so tapdisk2 12037 root mem REG 8,1 164708 180168 /usr/lib64/libxenctrl.so.4.0.0 tapdisk2 12037 root mem REG 8,1 18832 267724 /lib64/libuuid.so.1.3.0 tapdisk2 12037 root mem REG 8,1 410267 180118 /usr/lib64/libvhd.so.1.0.0 tapdisk2 12037 root mem REG 8,1 88368 268110 /lib64/libz.so.1.2.3 tapdisk2 12037 root mem REG 8,1 35656 267750 /lib64/librt-2.11.2.so tapdisk2 12037 root mem REG 8,1 128416 267762 /lib64/ld-2.11.2.so tapdisk2 12037 root mem CHR 251,0 44028 /dev/xen/blktap-2/blktap0 
tapdisk2 12037 root    0u   CHR                1,3      0t0   1539 /dev/null
tapdisk2 12037 root    1u   CHR                1,3      0t0   1539 /dev/null
tapdisk2 12037 root    2u   CHR                1,3      0t0   1539 /dev/null
tapdisk2 12037 root 3u unix 0xffff880039c862c0 0t0 44033 /var/run/blktap-control/ctl12037 tapdisk2 12037 root 4u 0000 0,8 0 1000 anon_inode 
tapdisk2 12037 root    5u  unix 0xffff880039cbe840      0t0  44036 socket
tapdisk2 12037 root 7u CHR 251,0 0t0 44028 /dev/xen/blktap-2/blktap0 tapdisk2 12037 root 8u BLK 252,0 0t0 36899 /dev/mapper/nathanxenuk1
The /dev/mapper devices are coming from a dell md3200i, using open-iscsi 2.0.871 and multipath-tools-0.4.9-r2.
This is using the main xen 4.1.1 release, with jeremy's git dom0 kernel (2.6.32.43). 

Anyone have any idea what might be happening here?

- Nathan

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