Hi Steve,
This series looks good to me.
Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
for this series.
Thank you!
# Now I know why sometimes func-graph depth looks broken...
On Wed, 21 Nov 2018 19:28:01 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> While working on rewriting function graph tracer, I found a design
> flaw in the code. Commit 03274a3ffb449 ("tracing/fgraph: Adjust fgraph depth
> before calling trace return callback") tried to fix a bug that caused
> interrupts not to be traced if max_depth was set to 1 (for debugging
> NO_HZ_FULL), because if it came in just as another function that was being
> traced that had a depth of 1 was exiting. This caused the timing of being in
> the kernel to be off. The fix was simply to move the calling of the return
> function after the updating of curr_ret_stack index as that was what was
> being used.
>
> The change log even says that it was safe to do this, but unfortunately it
> was not, and the barrier() there was specifically *for* that function (which
> shows why one should document barriers).
>
> The problem is that the return callback may still be using what's on the
> shadow stack and by changing the shadow stack pointer, it may allow for
> another function being traced to overwrite that data. Note, if this happens,
> it will only cause garbage data to be traced and will not affect the actual
> operations of the kernel (ie. it wont crash).
>
> Unfortunately just reverting that will bring back the old bug. The real way
> to fix that old bug is to create another counter to handle the depth, but
> this means that we need to change all the architectures that implement
> function graph tracing (that's 12 of them). Luckily, I need to do this
> anyway in my re-design so this is a good thing.
>
> Since all the archictectures do basicall the same thing to prepare the
> function graph trace to be traced, I made a generic function that they all
> can use and simplified the logic of all the architectures. Then I'm able to
> fix the design problem in one place.
>
> I pushed this code up to let zero-day have a whack at it, and I also
> downloaded the latest 8.1.0 cross compilers for all the archs that are
> affected and compiled tested them all (and got rid of all the warnings
> I introduced as well).
>
> I marked this all for stable, but in reality it may not need to be ported
> as it will probably not be trivial to do so, becaues you'll need to also
> fix the architectures that are no longer used (although do we care about
> them?). But if someone really cares about correct timings of the function
> graph profiler when the options/graph-time is set to zero, then be my
> guest.
>
> Feel free to test this! I'll be pushing this to linux-next and let it
> sit there a week or so before pushing it to Linus.
>
> git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> ftrace/urgent
>
> Head SHA1: 1ffd62e282a649483afb0bb4d76f7244b3c10075
>
>
> Steven Rostedt (VMware) (18):
> function_graph: Create function_graph_enter() to consolidate architecture code
> x86/function_graph: Simplify with function_graph_entry()
> ARM: function_graph: Simplify with function_graph_entry()
> arm64: function_graph: Simplify with function_graph_entry()
> microblaze: function_graph: Simplify with function_graph_entry()
> MIPS: function_graph: Simplify with function_graph_entry()
> nds32: function_graph: Simplify with function_graph_entry()
> parisc: function_graph: Simplify with function_graph_entry()
> powerpc/function_graph: Simplify with function_graph_entry()
> riscv/function_graph: Simplify with function_graph_entry()
> s390/function_graph: Simplify with function_graph_entry()
> sh/function_graph: Simplify with function_graph_entry()
> sparc/function_graph: Simplify with function_graph_entry()
> function_graph: Make ftrace_push_return_trace() static
> function_graph: Use new curr_ret_depth to manage depth instead of curr_ret_stack
> function_graph: Move return callback before update of curr_ret_stack
> function_graph: Reverse the order of pushing the ret_stack and the callback
> function_graph: Have profiler use curr_ret_stack and not depth
>
> ----
> arch/arm/kernel/ftrace.c | 17 +------------
> arch/arm64/kernel/ftrace.c | 15 +----------
> arch/microblaze/kernel/ftrace.c | 15 ++---------
> arch/mips/kernel/ftrace.c | 14 ++---------
> arch/nds32/kernel/ftrace.c | 18 ++-----------
> arch/parisc/kernel/ftrace.c | 17 +++----------
> arch/powerpc/kernel/trace/ftrace.c | 15 ++---------
> arch/riscv/kernel/ftrace.c | 14 ++---------
> arch/s390/kernel/ftrace.c | 13 ++--------
> arch/sh/kernel/ftrace.c | 16 ++----------
> arch/sparc/kernel/ftrace.c | 11 +-------
> arch/x86/kernel/ftrace.c | 15 +----------
> include/linux/ftrace.h | 4 +--
> include/linux/sched.h | 1 +
> kernel/trace/ftrace.c | 7 ++++--
> kernel/trace/trace_functions_graph.c | 49 ++++++++++++++++++++++++++++--------
> 16 files changed, 67 insertions(+), 174 deletions(-)
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
