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Subject[190/272] powerpc: Fix hcall tracepoint recursion
2.6.37-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
@@ -701,6 +701,13 @@ 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++;
@@ -713,12 +720,42 @@ 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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