[Bug runtime/24416] New: Tests stuck in uprobes_onthefly.exp

["wcohen at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=24416

            Bug ID: 24416
           Summary: Tests stuck in uprobes_onthefly.exp
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: wcohen at redhat dot com
  Target Milestone: ---

When running the "make installcheck" on multiple x86 machines running Fedora 29
and rawhide see that the tests getting stuck when running uprobes_onthefly.exp.
See multiple messages in the output of dmesg of the form from a rawhide machine
running kernel-5.0.5-300.fc30.x86_64:

[86154.130199] INFO: rcu_tasks detected stalls on tasks:
[86154.130202] 00000000c3a1580f: .. nvcsw: 0/0 holdout: 1 idle_cpu: -1/0
[86154.130204] uprobes_onthefl R  running task        0  7087  25897 0x00000000
[86154.130206] Call Trace:
[86154.130212]  ? __schedule+0x264/0x8a0
[86154.130213]  schedule+0x32/0x70
[86154.130215]  exit_to_usermode_loop+0x5c/0xd0
[86154.130217]  prepare_exit_to_usermode+0x59/0x60
[86154.130218]  retint_user+0x8/0x8
[86154.130220] RIP: 0033:0x40113c
[86154.130221] Code: fc 8b 45 ec 8d 14 00 8b 45 fc 01 d0 5d c3 55 48 89 e5 48
83 ec 10 89 7d fc 48 89 75 f0 8b 45 fc 89 c7 e8 cd ff ff ff 89 45 fc <eb> f1 66
90 f3 0f 1e fa 41 57 4c 8d 3d 03 2d 00 00 41 56 49 89 d6
[86154.130222] RSP: 002b:00007ffc66707c60 EFLAGS: 00000286 ORIG_RAX:
ffffffffffffff13
[86154.130223] RAX: 0000000099be4f1b RBX: 0000000000000000 RCX:
00007fe04acdc738
[86154.130223] RDX: 0000000011298a12 RSI: 00007ffc66707d58 RDI:
000000008894c509
[86154.130224] RBP: 00007ffc66707c70 R08: 00007fe04acddd80 R09:
00007fe04ad0f170
[86154.130224] R10: 0000000000000000 R11: 0000000000000022 R12:
0000000000401020
[86154.130225] R13: 00007ffc66707d50 R14: 0000000000000000 R15:
0000000000000000

Can reproduce with:

sudo make installcheck RUNTESTFLAGS="--debug
systemtap.onthefly/uprobes_onthefly.exp"

Looking at the traceback it looks like things could get stuck in
exit_to_usermode_loop if _TIF_NEED_RESCHED never gets set to zero.

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