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[Bug kprobes/2068] return probe on __switch_to triggers BUG_ON
- From: "jkenisto at us dot ibm dot com" <sourceware-bugzilla at sourceware dot org>
- To: systemtap at sources dot redhat dot com
- Date: 20 Dec 2005 23:43:22 -0000
- Subject: [Bug kprobes/2068] return probe on __switch_to triggers BUG_ON
- References: <20051219195313.2068.jkenisto@us.ibm.com>
- Reply-to: sourceware-bugzilla at sourceware dot org
------- Additional Comments From jkenisto at us dot ibm dot com 2005-12-20 23:43 -------
Some ppc64 data, only partially analyzed...
I tracked __switch_to calls and returns on a ppc64 system. Here __switch_to
does change the value of current (it matches prev on entry and new on return),
but the BUG_ON never gets triggered.
I also consistently see more calls than returns; and it's apparently not
entirely (or even mostly) due to running out of kretprobe_instance objects or
the entry probe getting installed before the return probe. Here are results
from various runs:
run# maxactive nmissed ncalls nret ncalls-(nret+nmissed)
1 5 112 209 92 5
2 50 0 293 267 26
3 50 0 406 364 42
4 50 0 759 717 42
5 50 0 1581 1535 46
6 50 173 7308 7055 80
Following the activity on a particular CPU, I occasionally see multiple
consecutive calls with no intervening returns.
--
http://sourceware.org/bugzilla/show_bug.cgi?id=2068
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