markers: fix markers read barrier for multiple probes (5def9a3a) · Commits · 戴 / test

Paul pointed out two incorrect read barriers in the marker handler code in the path where multiple probes are connected. Those are ordering reads of "ptype" (single or multi probe marker), "multi" array pointer, and "multi" array data access. It should be ordered like this : read ptype smp_rmb() read multi array pointer smp_read_barrier_depends() access data referenced by multi array pointer The code with a single probe connected (optimized case, does not have to allocate an array) has correct memory ordering. It applies to kernel 2.6.26.x, 2.6.25.x and linux-next. Signed-off-by:

Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: <stable@kernel.org> [2.6.25.x, 2.6.26.x] Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/marker.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -125,6 +125,11 @@ void marker_probe_cb(const struct marker mdata, void call_private, ...)
		} else {
		struct marker_probe_closure *multi;
		int i;
		/*
		* Read mdata->ptype before mdata->multi.
		*/
		smp_rmb();
		multi = mdata->multi;
		/*
		* multi points to an array, therefore accessing the array
		* depends on reading multi. However, even in this case,
		@@ -133,7 +138,6 @@ void marker_probe_cb(const struct marker mdata, void call_private, ...)
		* in the fast path, so put the explicit barrier here.
		*/
		smp_read_barrier_depends();
		multi = mdata->multi;
		for (i = 0; multi[i].func; i++) {
		va_start(args, call_private);
		multi[i].func(multi[i].probe_private, call_private,
		@@ -174,6 +178,11 @@ void marker_probe_cb_noarg(const struct marker mdata, void call_private, ...)
		} else {
		struct marker_probe_closure *multi;
		int i;
		/*
		* Read mdata->ptype before mdata->multi.
		*/
		smp_rmb();
		multi = mdata->multi;
		/*
		* multi points to an array, therefore accessing the array
		* depends on reading multi. However, even in this case,
		@@ -182,7 +191,6 @@ void marker_probe_cb_noarg(const struct marker mdata, void call_private, ...)
		* in the fast path, so put the explicit barrier here.
		*/
		smp_read_barrier_depends();
		multi = mdata->multi;
		for (i = 0; multi[i].func; i++)
		multi[i].func(multi[i].probe_private, call_private,
		mdata->format, &args);

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