Messages in this thread | | | Date | Sat, 20 Jun 2009 18:26:27 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 0/2] [GIT PULL][for 2.6.31] function graph gcc issue |
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* Steven Rostedt <rostedt@goodmis.org> wrote:
> Ingo, > > The bug I spent two days debugging that Jake found was due to gcc > making a copy of the return address into the stack frame and not > using it to actually return. The function graph tracer would > modify the copy and not the actual location that was used to > return to. Thus the accounting of the function graph tracer was > corrupted and a nasty crash followed. > > I found that 32bit x86 when compiled with optimize for size caused > this issue in the latest gcc (4.4.0). The first patch makes the > function graph tracer depend on !X86_32 || !CC_OPTIMIZE_FOR_SIZE. > This way we keep from getting into trouble with a know > configuration that breaks. > > Then next patch adds to x86 (both 32bit and 64bit) a test of the > frame pointer to make sure that the return actually goes to where > we expect it to. > > When debugging Jakes bug, The first instance was easy to find. It was > the timer_stats_update_stats that had a forced cacheline struct as a local. > I changed that and it seemed to fix the boot up test. When I enabled > function graph at run time, the system crashed again, but this time the > crash was hard to find where the issue was. I wrote up this test (patch 2) > and I found the problem immediately. In case gcc changes, we want to be > able to detect it right away before the tracer does anything dangerous. > > > Please pull the latest tip/tracing/urgent-1 tree, which can be found at: > > git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git > tip/tracing/urgent-1 > > > Steven Rostedt (2): > function-graph: disable when both x86_32 and optimize for size are configured > function-graph: add stack frame test > > ---- > arch/powerpc/kernel/ftrace.c | 2 +- > arch/s390/kernel/ftrace.c | 2 +- > arch/x86/Kconfig | 1 + > arch/x86/kernel/entry_32.S | 2 + > arch/x86/kernel/entry_64.S | 2 + > arch/x86/kernel/ftrace.c | 6 +++- > include/linux/ftrace.h | 4 ++- > kernel/trace/Kconfig | 8 +++++++ > kernel/trace/trace_functions_graph.c | 36 ++++++++++++++++++++++++++++++--- > 9 files changed, 54 insertions(+), 9 deletions(-) > --
Pulled, thanks Steve!
What a nasty bug ...
Ingo
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