sysctl: Fix data races in proc_dointvec_jiffies().

A sysctl variable is accessed concurrently, and there is always a chance
of data-race.  So, all readers and writers need some basic protection to
avoid load/store-tearing.

This patch changes proc_dointvec_jiffies() to use READ_ONCE() and
WRITE_ONCE() internally to fix data-races on the sysctl side.  For now,
proc_dointvec_jiffies() itself is tolerant to a data-race, but we still
need to add annotations on the other subsystem's side.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8c55ba01f41b6df6c829924ecd2e60236c5384c9..bf9383d17e1bb6f81bafcb9061ff3156045b7683 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1173,9 +1173,12 @@ static int do_proc_dointvec_jiffies_conv(bool *negp, unsigned long *lvalp,
        if (write) {
                if (*lvalp > INT_MAX / HZ)
                        return 1;
-               *valp = *negp ? -(*lvalp*HZ) : (*lvalp*HZ);
+               if (*negp)
+                       WRITE_ONCE(*valp, -*lvalp * HZ);
+               else
+                       WRITE_ONCE(*valp, *lvalp * HZ);
        } else {
-               int val = *valp;
+               int val = READ_ONCE(*valp);
                unsigned long lval;
                if (val < 0) {
                        *negp = true;