[Bug runtime/13514] New: more robust -rt support

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

http://sourceware.org/bugzilla/show_bug.cgi?id=13514

             Bug #: 13514
           Summary: more robust -rt support
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap@sourceware.org
        ReportedBy: fche@redhat.com
    Classification: Unclassified


One possible reason for systemtap -vs- kernel-rt instability could be this
lockdep message.

[ 3484.070463] 
[ 3484.070465] =================================
[ 3484.075050] [ INFO: inconsistent lock state ]
[ 3484.077048] 2.6.33.9-rt31.64.el5rtdebug #1
[ 3484.078345] ---------------------------------
[ 3484.080294] inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
[ 3484.083291] swapper/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
[ 3484.085296]  (_stp_print_lock#2){?.+...}, at: [<ffffffffa059c297>]
stp_print_flush+0x4b/0x1f4 [stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.091291] {HARDIRQ-ON-W} state was registered at:
[ 3484.093292]   [<ffffffff81075b09>] __lock_acquire+0x32f/0xc79
[ 3484.096291]   [<ffffffff81076524>] lock_acquire+0xd1/0xee
[ 3484.101296]   [<ffffffff8137bc18>] rt_spin_lock+0x43/0x48
[ 3484.105287]   [<ffffffffa059c297>] stp_print_flush+0x4b/0x1f4
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.110295]   [<ffffffffa059c46c>] _stp_print_flush+0x2c/0x31
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.115333]   [<ffffffffa059e47a>] probe_2000+0x3f/0x118
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.120303]   [<ffffffffa059fb9d>] enter_be_probe+0x117/0x1fc
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.125300]   [<ffffffffa05a148a>] _stp_ctl_write_cmd+0x3e0/0xf25
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.129300]   [<ffffffff81108ac0>] vfs_write+0xb3/0x10d
[ 3484.133326]   [<ffffffff81108be4>] sys_write+0x4f/0x77
[ 3484.136309]   [<ffffffff81002d1b>] system_call_fastpath+0x16/0x1b
[ 3484.141286] irq event stamp: 33336926
[ 3484.143287] hardirqs last  enabled at (33336925): [<ffffffff8100a25f>]
default_idle+0x39/0x55
[ 3484.148288] hardirqs last disabled at (33336926): [<ffffffff81002b97>]
save_args+0x67/0x70
[ 3484.154174] softirqs last  enabled at (0): [<ffffffff81043d8e>]
copy_process+0x5e3/0x139b
[ 3484.158290] softirqs last disabled at (0): [<(null)>] (null)
[ 3484.160286] 
[ 3484.160286] other info that might help us debug this:
[ 3484.166310] no locks held by swapper/0.
[ 3484.168288] 
[ 3484.168288] stack backtrace:
[ 3484.172304] Pid: 0, comm: swapper Tainted: G        W  
2.6.33.9-rt31.64.el5rtdebug #1
[ 3484.177293] Call Trace:
[ 3484.179168]  <IRQ>  [<ffffffff81073de0>] valid_state+0x17c/0x18f
[ 3484.182316]  [<ffffffff81073be6>] ? check_usage_forwards+0x0/0x7e
[ 3484.185388]  [<ffffffff81073ece>] mark_lock+0xdb/0x1f8
[ 3484.188167]  [<ffffffff81075a9a>] __lock_acquire+0x2c0/0xc79
[ 3484.190288]  [<ffffffff81068648>] ? cpu_clock+0x2d/0x41
[ 3484.192285]  [<ffffffff81076524>] lock_acquire+0xd1/0xee
[ 3484.197170]  [<ffffffffa059c297>] ? stp_print_flush+0x4b/0x1f4
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.202046]  [<ffffffff810708f2>] ? tick_sched_timer+0x0/0xa2
[ 3484.204338]  [<ffffffff8137bc18>] rt_spin_lock+0x43/0x48
[ 3484.207282]  [<ffffffffa059c297>] ? stp_print_flush+0x4b/0x1f4
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.211286]  [<ffffffffa059c297>] stp_print_flush+0x4b/0x1f4
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.215286]  [<ffffffff810708f2>] ? tick_sched_timer+0x0/0xa2
[ 3484.218289]  [<ffffffffa059c46c>] _stp_print_flush+0x2c/0x31
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.225202]  [<ffffffffa059eb41>] probe_2005+0x62/0xc5
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.230291]  [<ffffffffa059f698>] enter_profile_probes+0x297/0x2f4
[stap_dce4e96d74ad5bd334a54aae76da7bbb_4605]
[ 3484.234294]  [<ffffffff8106a657>] profile_tick+0x2e/0x6f
[ 3484.237236]  [<ffffffff81070974>] tick_sched_timer+0x82/0xa2
[ 3484.239287]  [<ffffffff81065c44>] __run_hrtimer+0xa4/0x134
[ 3484.242172]  [<ffffffff810660bf>] hrtimer_interrupt+0xde/0x1e3
[ 3484.244402]  [<ffffffff8138197a>] smp_apic_timer_interrupt+0x78/0x8b
[ 3484.247286]  [<ffffffff81003713>] apic_timer_interrupt+0x13/0x20
[ 3484.250219]  <EOI>  [<ffffffff8137f675>] ?
__atomic_notifier_call_chain+0x0/0x99
[ 3484.254320]  [<ffffffff8100a261>] ? default_idle+0x3b/0x55
[ 3484.258300]  [<ffffffff8100a25f>] ? default_idle+0x39/0x55
[ 3484.261293]  [<ffffffff81001f61>] cpu_idle+0x8d/0xe4
[ 3484.264287]  [<ffffffff81375453>] start_secondary+0x1ae/0x1b3

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