Dennis, Chuck, I have below issue on the list of tracked regressions. What's the status? Has any progress been made? Or is this not really a regression and can be ignored? Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat) P.S.: As the Linux kernel's regression tracker I deal with a lot of reports and sometimes miss something important when writing mails like this. If that's the case here, don't hesitate to tell me in a public reply, it's in everyone's interest to set the public record straight. #regzbot poke ##regzbot unlink: https://bugzilla.kernel.org/show_bug.cgi?id=215890 On 17.05.22 16:02, Chuck Lever III wrote: >> 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.
