powerpc: Fix hcall tracepoint recursion

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>

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index f129040..8323f14 100644 (file)
--- 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