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    Subject[PATCH 3.10 026/139] powerpc/kprobes: Pause function_graph tracing during jprobes handling
    Date
    From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>

    commit a9f8553e935f26cb5447f67e280946b0923cd2dc upstream.

    This fixes a crash when function_graph and jprobes are used together.
    This is essentially commit 237d28db036e ("ftrace/jprobes/x86: Fix
    conflict between jprobes and function graph tracing"), but for powerpc.

    Jprobes breaks function_graph tracing since the jprobe hook needs to use
    jprobe_return(), which never returns back to the hook, but instead to
    the original jprobe'd function. The solution is to momentarily pause
    function_graph tracing before invoking the jprobe hook and re-enable it
    when returning back to the original jprobe'd function.

    Fixes: 6794c78243bf ("powerpc64: port of the function graph tracer")
    Cc: stable@vger.kernel.org
    Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
    Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
    Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    ---
    arch/powerpc/kernel/kprobes.c | 11 +++++++++++
    1 file changed, 11 insertions(+)

    diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
    index 11f5b03..762c10d 100644
    --- a/arch/powerpc/kernel/kprobes.c
    +++ b/arch/powerpc/kernel/kprobes.c
    @@ -529,6 +529,15 @@ int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
    regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
    #endif

    + /*
    + * jprobes use jprobe_return() which skips the normal return
    + * path of the function, and this messes up the accounting of the
    + * function graph tracer.
    + *
    + * Pause function graph tracing while performing the jprobe function.
    + */
    + pause_graph_tracing();
    +
    return 1;
    }

    @@ -551,6 +560,8 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
    * saved regs...
    */
    memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
    + /* It's OK to start function graph tracing again */
    + unpause_graph_tracing();
    preempt_enable_no_resched();
    return 1;
    }
    --
    2.8.0.rc2.1.gbe9624a
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