tracing/x86/xen: Remove zero data size trace events trace_xen_mmu_flush_tlb{_all}

commit 45dd9b0666a162f8e4be76096716670cf1741f0e upstream.

Doing an audit of trace events, I discovered two trace events in the xen
subsystem that use a hack to create zero data size trace events. This is not
what trace events are for. Trace events add memory footprint overhead, and
if all you need to do is see if a function is hit or not, simply make that
function noinline and use function tracer filtering.

Worse yet, the hack used was:

 __array(char, x, 0)

Which creates a static string of zero in length. There's assumptions about
such constructs in ftrace that this is a dynamic string that is nul
terminated. This is not the case with these tracepoints and can cause
problems in various parts of ftrace.

Nuke the trace events!

Link: http://lkml.kernel.org/r/20180509144605.5a220327@gandalf.local.home
Fixes: 95a7d76897c1e ("xen/mmu: Use Xen specific TLB flush instead of the generic one.")
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 85003e57b1a3a697a1142344a10ce6ff26978836..6ecb05699952e568f74056900d372d2c1a500d50 100644 (file)
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1283,8 +1283,6 @@ void xen_flush_tlb_all(void)
        struct mmuext_op *op;
        struct multicall_space mcs;
 
-       trace_xen_mmu_flush_tlb_all(0);
-
        preempt_disable();
 
        mcs = xen_mc_entry(sizeof(*op));
@@ -1297,13 +1295,11 @@ void xen_flush_tlb_all(void)
 
        preempt_enable();
 }
-static void xen_flush_tlb(void)
+static noinline void xen_flush_tlb(void)
 {
        struct mmuext_op *op;
        struct multicall_space mcs;
 
-       trace_xen_mmu_flush_tlb(0);
-
        preempt_disable();
 
        mcs = xen_mc_entry(sizeof(*op));

diff --git a/include/trace/events/xen.h b/include/trace/events/xen.h
index d06b6da5c1e3e146d500bae9b012b809d831cb25..79c42ed1bcb5a24f9cf54bc327398dd61f8f0a0f 100644 (file)
--- a/include/trace/events/xen.h
+++ b/include/trace/events/xen.h
@@ -377,22 +377,6 @@ DECLARE_EVENT_CLASS(xen_mmu_pgd,
 DEFINE_XEN_MMU_PGD_EVENT(xen_mmu_pgd_pin);
 DEFINE_XEN_MMU_PGD_EVENT(xen_mmu_pgd_unpin);
 
-TRACE_EVENT(xen_mmu_flush_tlb_all,
-           TP_PROTO(int x),
-           TP_ARGS(x),
-           TP_STRUCT__entry(__array(char, x, 0)),
-           TP_fast_assign((void)x),
-           TP_printk("%s", "")
-       );
-
-TRACE_EVENT(xen_mmu_flush_tlb,
-           TP_PROTO(int x),
-           TP_ARGS(x),
-           TP_STRUCT__entry(__array(char, x, 0)),
-           TP_fast_assign((void)x),
-           TP_printk("%s", "")
-       );
-
 TRACE_EVENT(xen_mmu_flush_tlb_single,
            TP_PROTO(unsigned long addr),
            TP_ARGS(addr),