From 5def9a3a22e09c99717f41ab7f07ec9e1a1f3ec8 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Tue, 29 Jul 2008 22:33:31 -0700 Subject: [PATCH] markers: fix markers read barrier for multiple probes 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 Cc: "Paul E. McKenney" Cc: [2.6.25.x, 2.6.26.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/marker.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/marker.c b/kernel/marker.c index 971da53179..7d1faecd7a 100644 --- a/kernel/marker.c +++ b/kernel/marker.c @@ -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); -- 2.39.5