[Bug tapsets/19001] New: mdelay() causing soft lockup

[Bug tapsets/19001] New: mdelay() causing soft lockup

[mcermak at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19001

            Bug ID: 19001
           Summary: mdelay() causing soft lockup
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tapsets
          Assignee: systemtap at sourceware dot org
          Reporter: mcermak at redhat dot com
  Target Milestone: ---

Following mdelay() invocation causes soft lockup using fresh stap bits
(d01bc760e1) on top of kernel-3.10.0-315.el7.x86_64:

=======
 7.2 S x86_64 # stap -vge 'probe oneshot {mdelay(-1)}'
Pass 1: parsed user script and 110 library script(s) using
214612virt/32028res/3132shr/29360data kb, in 370usr/0sys/370real ms.
Pass 2: analyzed script: 1 probe(s), 2 function(s), 1 embed(s), 0 global(s)
using 215404virt/33084res/3252shr/30152data kb, in 10usr/0sys/5real ms.
Pass 3: translated to C into
"/tmp/stapBujmUZ/stap_f07b99d863518b698843befea0531c3d_1318_src.c" using
215404virt/33420res/3552shr/30152data kb, in 0usr/0sys/0real ms.
Pass 4: compiled C into "stap_f07b99d863518b698843befea0531c3d_1318.ko" in
900usr/250sys/1054real ms.
Pass 5: starting run.

Message from syslogd@dhcp-1-112 at Sep 24 05:24:25 ...
 kernel:BUG: soft lockup - CPU#3 stuck for 23s! [stapio:8492]
=======

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[Bug tapsets/19001] mdelay() causing soft lockup

[bmr at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19001

Bryn M. Reeves <bmr at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bmr at redhat dot com

--- Comment #1 from Bryn M. Reeves <bmr at redhat dot com> ---
This is expected when passing -1 as the delay interval: I originally wrote the
tapset to allow controlled simulation of driver bugs that triggered
softlockups.

The guru-delay tapset is useful for introducing (normally short) controlled
delays at specified probe points; if the specified delay interval exceeds the
configured softlockup threshold for the system it will trigger these warnings.

This is the reason the tapset is named 'guru-delay' and requires -g to be used
- Frank suggested this name and restriction during review to prevent an
unprivileged user impacting other system activities.

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[Bug tapsets/19001] mdelay() causing soft lockup

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19001

Frank Ch. Eigler <fche at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |fche at redhat dot com
         Resolution|---                         |INVALID

--- Comment #2 from Frank Ch. Eigler <fche at redhat dot com> ---
Bryn is correct, this is working as designed.
Correct use of guru-mode tapset functions is the programmer's responsibility.

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