Messages in this thread | | | Date | Thu, 29 Oct 2009 16:51:51 -0400 | From | Steven Rostedt <> | Subject | [PATCH 0/3][RFC] tracing/kprobes: prevent jprobes from crashing function graph tracer |
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Lately I've been testing with an allyesconfig. When I ran the function graph tracer, it immediately crashed the kernel. Thanks to the new frame pointer test in function graph, it reported directly what the issue was and then panicked the kernel to prevent any unexpected damage from happening.
It pointed the error to be with jtcp_rcv_established. Which is a jprobe function added to tcp_rcv_established at bootup when CONFIG_NET_TCPPROBE is enabled.
Jprobes and the function graph tracer use the same mechanism to trace the exit of a function. Unfortunately, only one can be done at a time. The function graph tracer replaces the return address with its own handler, but so does jprobes. The two are not compatible.
The solution I am proposing with this patch set is to add a call in ftrace that lets other code in the kernel permanently disable functions from being traced by the function and function graph tracer. As a probe function is registered with jprobes, it calls this new function and that entry will be removed from being traced.
I tested this with this patch series and it does solve the problem.
Some issues though:
1) this only works when DYNAMIC_FTRACE is enabled. We can prevent function graph tracing with jprobes when DYNAMIC_FTRACE is not enabled through Kconfig dependencies. Or have the registering of a jprobe permanently disable function graph tracing.
2) This also prevents the function tracer from being able to trace a function probe, even though the function tracer is not at issue with this bug.
Feedback welcomed.
-- Steve
The following patches are in:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
branch: rfc/trace
Steven Rostedt (3): tracing: Clean up ftrace.h header and add ftrace_set_notrace() declaration tracing: Add calls to permanently disable functions from tracing tracing/kprobes: Disable tracing registered jprobe callback functions
---- include/linux/ftrace.h | 26 +++++++-- kernel/kprobes.c | 4 + kernel/trace/ftrace.c | 147 +++++++++++++++++++++++++++++++++++++++++------- 3 files changed, 150 insertions(+), 27 deletions(-)
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