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    Subject[patch 127/176] powerpc: Fix hcall tracepoint recursion
    2.6.36-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Anton Blanchard <anton@samba.org>

    commit 57cdfdf829a850a317425ed93c6a576c9ee6329c upstream.

    Spinlocks on shared processor partitions use H_YIELD to notify the
    hypervisor we are waiting on another virtual CPU. Unfortunately this means
    the hcall tracepoints can recurse.

    The patch below adds a percpu depth and checks it on both the entry and
    exit hcall tracepoints.

    Signed-off-by: Anton Blanchard <anton@samba.org>
    Acked-by: Steven Rostedt <rostedt@goodmis.org>
    Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    arch/powerpc/platforms/pseries/lpar.c | 37 ++++++++++++++++++++++++++++++++++
    1 file changed, 37 insertions(+)

    --- a/arch/powerpc/platforms/pseries/lpar.c
    +++ b/arch/powerpc/platforms/pseries/lpar.c
    @@ -680,6 +680,13 @@ EXPORT_SYMBOL(arch_free_page);
    /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
    extern long hcall_tracepoint_refcount;

    +/*
    + * Since the tracing code might execute hcalls we need to guard against
    + * recursion. One example of this are spinlocks calling H_YIELD on
    + * shared processor partitions.
    + */
    +static DEFINE_PER_CPU(unsigned int, hcall_trace_depth);
    +
    void hcall_tracepoint_regfunc(void)
    {
    hcall_tracepoint_refcount++;
    @@ -692,12 +699,42 @@ void hcall_tracepoint_unregfunc(void)

    void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
    {
    + unsigned long flags;
    + unsigned int *depth;
    +
    + local_irq_save(flags);
    +
    + depth = &__get_cpu_var(hcall_trace_depth);
    +
    + if (*depth)
    + goto out;
    +
    + (*depth)++;
    trace_hcall_entry(opcode, args);
    + (*depth)--;
    +
    +out:
    + local_irq_restore(flags);
    }

    void __trace_hcall_exit(long opcode, unsigned long retval,
    unsigned long *retbuf)
    {
    + unsigned long flags;
    + unsigned int *depth;
    +
    + local_irq_save(flags);
    +
    + depth = &__get_cpu_var(hcall_trace_depth);
    +
    + if (*depth)
    + goto out;
    +
    + (*depth)++;
    trace_hcall_exit(opcode, retval, retbuf);
    + (*depth)--;
    +
    +out:
    + local_irq_restore(flags);
    }
    #endif



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