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Subject[PATCH tip/core/rcu 55/55] powerpc: Work around tracing from dyntick-idle mode
Date
PowerPC LPAR's __trace_hcall_exit() can invoke event tracing at a
point where RCU has been told that the CPU is in dyntick-idle mode.
Because event tracing uses RCU, this can result in failures.

A correct fix would arrange for RCU to be told about dyntick-idle
mode after tracing had completed, however, this will require some care
because it appears that __trace_hcall_exit() can also be called from
non-dyntick-idle mode.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: anton@samba.org
Cc: benh@kernel.crashing.org
Cc: paulus@samba.org
---
arch/powerpc/platforms/pseries/lpar.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 39e6e0a..668f300 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -715,12 +715,14 @@ EXPORT_SYMBOL(arch_free_page);
/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
extern long hcall_tracepoint_refcount;

+#if 0 /* work around buggy use of RCU from dyntick-idle mode */
/*
* 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);
+#endif /* #if 0 work around buggy use of RCU from dyntick-idle mode */

void hcall_tracepoint_regfunc(void)
{
@@ -734,6 +736,7 @@ void hcall_tracepoint_unregfunc(void)

void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
{
+#if 0 /* work around buggy use of RCU from dyntick-idle mode */
unsigned long flags;
unsigned int *depth;

@@ -750,11 +753,13 @@ void __trace_hcall_entry(unsigned long opcode, unsigned long *args)

out:
local_irq_restore(flags);
+#endif /* #if 0 work around buggy use of RCU from dyntick-idle mode */
}

void __trace_hcall_exit(long opcode, unsigned long retval,
unsigned long *retbuf)
{
+#if 0 /* work around buggy use of RCU from dyntick-idle mode */
unsigned long flags;
unsigned int *depth;

@@ -771,6 +776,7 @@ void __trace_hcall_exit(long opcode, unsigned long retval,

out:
local_irq_restore(flags);
+#endif /* #if 0 work around buggy use of RCU from dyntick-idle mode */
}
#endif

--
1.7.3.2


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