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If the function graph tracer traces a jprobe callback, the system will crash. This can easily be demonstrated by compiling the jprobe sample module that is in the kernel tree, loading it and running the function graph tracer. # modprobe jprobe_example.ko # echo function_graph > /sys/kernel/debug/tracing/current_tracer # ls The first two commands end up in a nice crash after the first fork. (do_fork has a jprobe attached to it, so "ls" just triggers that fork) The problem is caused by the jprobe_return() that all jprobe callbacks must end with. The way jprobes works is that the function a jprobe is attached to has a breakpoint placed at the start of it (or it uses ftrace if fentry is supported). The breakpoint handler (or ftrace callback) will copy the stack frame and change the ip address to return to the jprobe handler instead of the function. The jprobe handler must end with jprobe_return() which swaps the stack and does an int3 (breakpoint). This breakpoint handler will then put back the saved stack frame, simulate the instruction at the beginning of the function it added a breakpoint to, and then continue on. For function tracing to work, it hijakes the return address from the stack frame, and replaces it with a hook function that will trace the end of the call. This hook function will restore the return address of the function call. If the function tracer traces the jprobe handler, the hook function for that handler will not be called, and its saved return address will be used for the next function. This will result in a kernel crash. To solve this, pause function tracing before the jprobe handler is called and unpause it before it returns back to the function it probed. Some other updates: Used a variable "saved_sp" to hold kcb->jprobe_saved_sp. This makes the code look a bit cleaner and easier to understand (various tries to fix this bug required this change). Note, if fentry is being used, jprobes will change the ip address before the function graph tracer runs and it will not be able to trace the function that the jprobe is probing. Link: http://lkml.kernel.org/r/20150114154329.552437962@goodmis.org Cc: stable@vger.kernel.org # 2.6.30+ Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> |
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| .. | ||
| common.h | ||
| core.c | ||
| ftrace.c | ||
| Makefile | ||
| opt.c | ||