time: jiffies_delta_to_clock_t() helper to the rescue

Various /proc/net files sometimes report crazy timer values, expressed
in clock_t units.

This happens when an expired timer delta (expires - jiffies) is passed
to jiffies_to_clock_t().

This function has an overflow in :

return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);

commit cbbc719fccdb8cb (time: Change jiffies_to_clock_t() argument type
to unsigned long) only got around the problem.

As we cant output negative values in /proc/net/tcp without breaking
various tools, I suggest adding a jiffies_delta_to_clock_t() wrapper
that caps the negative delta to a 0 value.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Maciej Żenczykowski <maze@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: hank <pyu@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 2 insertions, 2 deletions

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index d21f32383517..9ce430b4657c 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -312,7 +312,7 @@ int br_fdb_fillbuf(struct net_bridge *br, void *buf,
 
                         fe->is_local = f->is_local;
                         if (!f->is_static)
-                                fe->ageing_timer_value = jiffies_to_clock_t(jiffies - f->updated);
+                                fe->ageing_timer_value = jiffies_delta_to_clock_t(jiffies - f->updated);
                         ++fe;
                         ++num;
                 }
diff --git a/net/bridge/br_stp_timer.c b/net/bridge/br_stp_timer.c
index a6747e673426..c3530a81a33b 100644
--- a/net/bridge/br_stp_timer.c
+++ b/net/bridge/br_stp_timer.c
@@ -170,5 +170,5 @@ void br_stp_port_timer_init(struct net_bridge_port *p)
 unsigned long br_timer_value(const struct timer_list *timer)
 {
         return timer_pending(timer)
-                ? jiffies_to_clock_t(timer->expires - jiffies) : 0;
+                ? jiffies_delta_to_clock_t(timer->expires - jiffies) : 0;
 }