> On May 17, 2022, at 9:40 AM, Dennis Dalessandro <dennis.dalessandro@xxxxxxxxxxxxxxxxxxxx> wrote: > > On 5/13/22 10:59 AM, Chuck Lever III wrote: >>>> >>>> Ran a test with -rc6 and this time see a hung task trace on the >>>> console as well >>>> as an NFS RPC error. >>>> >>>> [32719.991175] nfs: RPC call returned error 512 >>>> . >>>> . >>>> . >>>> [32933.285126] INFO: task kworker/u145:23:886141 blocked for more >>>> than 122 seconds. >>>> [32933.293543] Tainted: G S 5.18.0-rc6 #1 >>>> [32933.299869] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" >>>> disables this >>>> message. >>>> [32933.308740] task:kworker/u145:23 state:D stack: 0 pid:886141 >>>> ppid: 2 >>>> flags:0x00004000 >>>> [32933.318321] Workqueue: rpciod rpc_async_schedule [sunrpc] >>>> [32933.324524] Call Trace: >>>> [32933.327347] <TASK> >>>> [32933.329785] __schedule+0x3dd/0x970 >>>> [32933.333783] schedule+0x41/0xa0 >>>> [32933.337388] xprt_request_dequeue_xprt+0xd1/0x140 [sunrpc] >>>> [32933.343639] ? prepare_to_wait+0xd0/0xd0 >>>> [32933.348123] ? rpc_destroy_wait_queue+0x10/0x10 [sunrpc] >>>> [32933.354183] xprt_release+0x26/0x140 [sunrpc] >>>> [32933.359168] ? rpc_destroy_wait_queue+0x10/0x10 [sunrpc] >>>> [32933.365225] rpc_release_resources_task+0xe/0x50 [sunrpc] >>>> [32933.371381] __rpc_execute+0x2c5/0x4e0 [sunrpc] >>>> [32933.376564] ? __switch_to_asm+0x42/0x70 >>>> [32933.381046] ? finish_task_switch+0xb2/0x2c0 >>>> [32933.385918] rpc_async_schedule+0x29/0x40 [sunrpc] >>>> [32933.391391] process_one_work+0x1c8/0x390 >>>> [32933.395975] worker_thread+0x30/0x360 >>>> [32933.400162] ? process_one_work+0x390/0x390 >>>> [32933.404931] kthread+0xd9/0x100 >>>> [32933.408536] ? kthread_complete_and_exit+0x20/0x20 >>>> [32933.413984] ret_from_fork+0x22/0x30 >>>> [32933.418074] </TASK> >>>> >>>> The call trace shows up again at 245, 368, and 491 seconds. Same >>>> task, same trace. >>>> >>>> >>>> >>>> >>> >>> That's very helpful. The above trace suggests that the RDMA code is >>> leaking a call to xprt_unpin_rqst(). >> >> IMHO this is unlikely to be related to the performance >> regression -- none of this code has changed in the past 5 >> kernel releases. Could be a different issue, though. >> >> As is often the case in these situations, the INFO trace >> above happens long after the issue that caused the missing >> unpin. So... unless Dennis has a reproducer that can trigger >> the issue frequently, I don't think there's much that can >> be extracted from that. > > To be fair, I've only seen this one time and have had the performance regression > since -rc1. > >> Also "nfs: RPC call returned error 512" suggests someone >> hit ^C at some point. It's always possible that the >> xprt_rdma_free() path is missing an unpin. But again, >> that's not likely to be related to performance. > > I've checked our test code and after 10 minutes it does give up trying to do the > NFS copies and aborts (SIG_INT) the test. After sleeping on it, I'm fairly certain the stack trace above is a result of a gap in how xprtrdma handles a signaled RPC. Signal handling in that code is pretty hard to test, so not surprising that there's a lingering bug or two. One idea I had was to add a fault injector in the RPC scheduler to throw signals at random. I think it can be done without perturbing the hot path. Maybe I'll post an RFC patch. > So in all my tests and bisect attempts it seems the possibility to hit a slow > NFS operation that hangs for minutes has been possible for quite some time. > However in 5.18 it gets much worse. > > Any likely places I should add traces to try and find out what's stuck or taking > time? There's been a lot of churn in that area in recent releases, so I'm not familiar with the existing tracepoints. Maybe Ben or Trond could provide some guidance. -- Chuck Lever
