Details
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Bug
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Resolution: Fixed
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Blocker
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Lustre 2.4.0
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3
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5413
Description
The IO nodes on Sequoia are going unresponsive with many CPU soft lockup messages in the logs. For example, a couple messages from a node in this state are as follows:
2012-11-01 23:44:47.681648 {DefaultControlEventListener} [mmcs]{161}.0.2: BUG: soft lockup - CPU#2 stuck for 67s! [ptlrpcd_56:3326]
2012-11-01 23:44:47.720983 {DefaultControlEventListener} [mmcs]{161}.0.2: Modules linked in: lmv(U) mgc(U) lustre(U) mdc(U) fid(U) fld(U) lov(U) osc(U) ko2iblnd(U) ptlrpc(U) obdclass(U) lnet(U) lvfs(U) libcfs(U) bgvrnic bgmudm
2012-11-01 23:44:47.760955 {DefaultControlEventListener} [mmcs]{161}.0.2: NIP: c00000000042e194 LR: 8000000003a674bc CTR: c00000000042e160
2012-11-01 23:44:47.801187 {DefaultControlEventListener} [mmcs]{161}.0.2: REGS: c0000003ca2e7900 TRAP: 0901 Not tainted (2.6.32-220.23.3.bgq.13llnl.V1R1M2.bgq62_16.ppc64)
2012-11-01 23:44:47.841287 {DefaultControlEventListener} [mmcs]{161}.0.2: MSR: 0000000080029000 <EE,ME,CE> CR: 84284444 XER: 20000000
2012-11-01 23:44:47.880979 {DefaultControlEventListener} [mmcs]{161}.0.2: TASK = c0000003ca1c7980[3326] 'ptlrpcd_56' THREAD: c0000003ca2e4000 CPU: 2
2012-11-01 23:44:47.921379 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR00: 0000000080000038 c0000003ca2e7b80 c0000000006de510 c0000003ceca6278
2012-11-01 23:44:47.960900 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR04: 0000000000000001 0000000000000000 0000000000000000 0000000000000000
2012-11-01 23:44:48.000948 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR08: 0000000000200200 0000000080000002 c0000003cefddc68 c00000000042e160
2012-11-01 23:44:48.105877 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR12: 8000000003aebdb8 c000000000743f00
2012-11-01 23:44:48.106188 {DefaultControlEventListener} [mmcs]{161}.0.2: NIP [c00000000042e194] ._spin_lock+0x34/0x44
2012-11-01 23:44:48.121006 {DefaultControlEventListener} [mmcs]{161}.0.2: LR [8000000003a674bc] .ptlrpc_check_set+0xeac/0x4e80 [ptlrpc]
2012-11-01 23:44:48.161100 {DefaultControlEventListener} [mmcs]{161}.0.2: Call Trace:
2012-11-01 23:44:48.201258 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca2e7b80] [8000000003a674ac] .ptlrpc_check_set+0xe9c/0x4e80 [ptlrpc] (unreliable)
2012-11-01 23:44:48.240907 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca2e7d20] [8000000003abd1dc] .ptlrpcd_check+0x66c/0x8a0 [ptlrpc]
2012-11-01 23:44:48.280969 {DefaultControlEventListener} [mmcs]{161}.0.2:
The line it's stuck on:
(gdb) l *ptlrpc_check_set+0xeac 0x474bc is in ptlrpc_check_set (/builddir/build/BUILD/lustre-2.3.54/lustre/ptlrpc/client.c:1666).
And the source level info:
1663 if (!ptlrpc_unregister_reply(req, 1))
1664 continue;
1665
1666 cfs_spin_lock(&imp->imp_lock);
1667 if (ptlrpc_import_delay_req(imp, req, &status)){
1668 /* put on delay list - only if we wait
1669 * recovery finished - before send */
Details of the next message on the console:
BUG: soft lockup - CPU#16 stuck for 67s! [ptlrpcd_rcv:3269]
2012-11-01 23:44:48.320953 {DefaultControlEventListener} [mmcs]{161}.0.2: Modules linked in: lmv(U) mgc(U) lustre(U) mdc(U) fid(U) fld(U) lov(U) osc(U) ko2iblnd(U) ptlrpc(U) obdclass(U) lnet(U) lvfs(U) libcfs(U) bgvrnic bgmudm
2012-11-01 23:44:48.361045 {DefaultControlEventListener} [mmcs]{161}.0.2: NIP: c00000000042e18c LR: 8000000003a66b04 CTR: c00000000042e160
2012-11-01 23:44:48.400942 {DefaultControlEventListener} [mmcs]{161}.0.2: REGS: c0000003ca203900 TRAP: 0901 Not tainted (2.6.32-220.23.3.bgq.13llnl.V1R1M2.bgq62_16.ppc64)
2012-11-01 23:44:48.440963 {DefaultControlEventListener} [mmcs]{161}.0.2: MSR: 0000000080029000 <EE,ME,CE> CR: 84228484 XER: 20000000
2012-11-01 23:44:48.480905 {DefaultControlEventListener} [mmcs]{161}.0.2: TASK = c0000003c5d432a0[3269] 'ptlrpcd_rcv' THREAD: c0000003ca200000 CPU: 16
2012-11-01 23:44:48.520898 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR00: 0000000080000038 c0000003ca203b80 c0000000006de510 c0000003ceca6278
2012-11-01 23:44:48.560925 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR04: 0000000000000001 0000000000000000 0000000000000000 0000000000000000
2012-11-01 23:44:48.600920 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR08: c0000003ceca6260 0000000080000010 c0000003ce673420 c00000000042e160
2012-11-01 23:44:48.640881 {DefaultControlEventListener} [mmcs]{161}.0.2: GPR12: 8000000003aebdb8 c00000000074f500
2012-11-01 23:44:48.680904 {DefaultControlEventListener} [mmcs]{161}.0.2: NIP [c00000000042e18c] ._spin_lock+0x2c/0x44
2012-11-01 23:44:48.720885 {DefaultControlEventListener} [mmcs]{161}.0.2: LR [8000000003a66b04] .ptlrpc_check_set+0x4f4/0x4e80 [ptlrpc]
2012-11-01 23:44:48.761372 {DefaultControlEventListener} [mmcs]{161}.0.2: Call Trace:
2012-11-01 23:44:48.800923 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca203b80] [8000000003a66974] .ptlrpc_check_set+0x364/0x4e80 [ptlrpc] (unreliable)
2012-11-01 23:44:48.840892 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca203d20] [8000000003abd1dc] .ptlrpcd_check+0x66c/0x8a0 [ptlrpc]
2012-11-01 23:44:48.880936 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca203e40] [8000000003abd76c] .ptlrpcd+0x35c/0x510 [ptlrpc]
2012-11-01 23:44:48.920887 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca203f90] [c00000000001a9e0] .kernel_thread+0x54/0x70
2012-11-01 23:44:48.961113 {DefaultControlEventListener} [mmcs]{161}.0.2: Instruction dump:
2012-11-01 23:44:49.000886 {DefaultControlEventListener} [mmcs]{161}.0.2: 4bffffc8 38000000 980d0c94 812d0000 7c001829 2c000000 40c20010 7d20192d
2012-11-01 23:44:49.040902 {DefaultControlEventListener} [mmcs]{161}.0.2: 40c2fff0 4c00012c 2fa00000 4dfe0020 <7c210b78> 80030000 2fa00000 40defff4
2012-11-01 23:44:49.121348 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca2e7e40] [8000000003abd76c] .ptlrpcd+0x35c/0x510 [ptlrpc]
2012-11-01 23:44:49.160915 {DefaultControlEventListener} [mmcs]{161}.0.2: [c0000003ca2e7f90] [c00000000001a9e0] .kernel_thread+0x54/0x70
2012-11-01 23:44:49.201038 {DefaultControlEventListener} [mmcs]{161}.0.2: Instruction dump:
2012-11-01 23:44:49.241229 {DefaultControlEventListener} [mmcs]{161}.0.2: 980d0c94 812d0000 7c001829 2c000000 40c20010 7d20192d 40c2fff0 4c00012c
2012-11-01 23:44:49.281578 {DefaultControlEventListener} [mmcs]{161}.0.2: 2fa00000 4dfe0020 7c210b78 80030000 <2fa00000> 40defff4 7c421378 4bffffc8
The line it's stuck on:
(gdb) l *ptlrpc_check_set+0x4f4 0x46b04 is in ptlrpc_check_set (/builddir/build/BUILD/lustre-2.3.54/lustre/ptlrpc/client.c:1852).
And the source level info:
1849 >------->------->-------libcfs_nid2str(imp->imp_connection->c_peer.nid), 1850 >------->------->-------lustre_msg_get_opc(req->rq_reqmsg)); 1851 1852 cfs_spin_lock(&imp->imp_lock); 1853 /* Request already may be not on sending or delaying list. This 1854 * may happen in the case of marking it erroneous for the case 1855 * ptlrpc_import_delay_req(req, status) find it impossible to
The symptoms look very similar to what we saw on the old Orion code base, which boiled down to "too many" ptlrpc threads contending with each other while interrupts were disabled. To get past that previous issue we pulled in a patch to limit the number of threads created, thus reducing the contention on the lock in question.
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And just to be clear, I believe that this WAS a deadlock situation, as detailed in this comment.
so, it's roughly 1.1/128 or ~9MB/s per OST on an average ION and actually very few RPC/second/import...
On writes, we currently see about 850 GB/s, so with 768 IONs that is roughly 1.1 GB/s per ION (the ION is the lustre client).
When I had problems, I was running an ior something like this:
ior -F -e -g -C -t 1m -b 512m -o /p/ls1/morrone/foo
The ior was 98,304 MPI tasks in size.
Under normal conditions, each Sequoia I/O Node (ION) handles I/O for 128 compute nodes. So a given ION will handle 128 files. We have currently left the filesystem default at 1-stripe per file, so each ION will be writing to up to 128 different OSTs at more-or-less the same time.
Christopher, Prakash, could you describe the workload and/or estimate it in RPC/second please ?
we usually limit number of RPCs in flight to 8 (per import). to achieve 1GB/s per OST with 1MB RPC we'd need 1024 RPC/second. say, we're grabbing imp_lock roughly 10 times for every processed RPC, which gives us to ~10K/sec lock instances. but this is in the case of 1GB/s going to a single OST.
I think it'd be helpful to collect data on CONFIG_LOCK_STAT-enabled kernel.
if this is not a deadlock, then I'd consider few possible contributors:
1) CDEBUG() overhead while imp_lock is held
2) cache ping-pong if OST_WRITE go to different partitions
3) a lot of non-committed requests making ptlrpc_free_committed() slow (which is running with imp_lock held)
4) lack of need_resched() in ptlrpc_check_set() (though in all listed cases it was in _spin_lock())
I was wrong in previous comment, CDEBUG will not disable interrupt if it's in thread context, but I still suggest to disable D_HA and D_IOCTL to see if it can help before we find any other clue, I remember a couple of years ago I saw some tests hit soft lockup while enabling D_INFO.
I have checked code and log again, but still didn't find any possible deadlock. Lustre only have very few cases will disable interrupt (I remember we used to take spin_lock_bh for imp_lock, but we have changed that a few years ago). However, CDEBUG will definitely disable interrupt, any we did call CDEBUG_REQ many times with hold of imp_lock, CDEBUG_REQ has complex format which makes it a little expensive, so one thing might be worth a try is, disable D_HA and D_IOCTL on clients to see if it can make any difference, at the meanwhile, I will check code again.
I attached an excerpt from the console log, file R01-ID-J06.log, for the time in question. Mostly there are sysiod processes stuck, but there is one ptlrpcd_rcv process in there at the beginning of the incident as well. Unfortunately, the backtrace of ptlrpcd_rcv is interleaved with a couple of other sysiod backtraces, so it is difficult to see where it was. But perhaps we can find the culprit in there somewhere.
Well, careful, I'm not sure that I believe that seeing the processes soft lockup in close() a few minutes before the reboot means what you think it means.
This was a 98,304 process ior running on Sequoia. That means 128 MPI tasks writing to lustre through one I/O Node (ION). Each ION has 68 "cpus" from Linux's perspective, 17 real cores, and 4-way SMP threading.
In the incident on ION R01-ID-J06, between the times of 2012-11-28 11:06:10.548123 and 2012-11-28 11:08:34.717051 (just over two minutes of time), I count at least 51 tasks that trigger soft lockup messages.
Then, nearly 40 minutes later and only 5 minutes before the node is shut down, I see only two new process that show soft lockups in new processes under the file close. But you'll note that these are not the same processes that were stuck in the fsync() earlier. Also note that these processes that get hung under close have their backtraces start at "do_signal".
I believe what is happening is that some, but not all, of the 128 processes get stuck in fsync. Perhaps around 50 in this instance. Some of the processes actually completed their fsync and are just sitting with the file descriptor open, doing nothing.
Then IBM's control system comes along and tries to shutdown the ION at the system administrator's request. One thing it likely did was send a signal to the sysiod tasks to shut them down. During the signal handling to kill the process, the kernel is going to clean up open file descriptors. When it tries to close the open lustre file descriptor, some processes now get stuck on the same lock as the others, but in the close() path rather than the fsync() path.
After some timeout (5 minutes probably), IBM's system stops waiting for there daemons to exit, and starts a shutdown of the whole node.
So I suspect that the processes really are stuck, and will never make progress.
I think it's just because imp_lock is under high contention if it's eventually cleared up 
, I don't have very good idea to improve this so far, but I will see want I can do.
this spinlock will not disable interrupts, but soft lockup will dump stack to console which is extremely slow and system might not responding .
I did find a deadlock....
ptlrpc_at_recv_early_reply() calls ptlrpc_at_set_req_timeout() with hold of ptlrpc_request::rq_lock, and ptlrpc_at_set_req_timeout()->import_at_get_index() requires imp_lock, it violates locking-order rule of Lustre, which assumes rq_lock can nest in imp_lock.
This is introduced by BZ16999
Path is here: http://review.whamcloud.com/#change,4880