[PATCH 4.4 15/92] tg3: Fix vunmap() BUG_ON() triggered from tg3_free_consistent().

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Chan <michael.c...@broadcom.com>

[ Upstream commit d89a2adb8bfe6f8949ff389acdb9fa298b6e8e12 ]

tg3_free_consistent() calls dma_free_coherent() to free tp->hw_stats
under spinlock and can trigger BUG_ON() in vunmap() because vunmap()
may sleep.  Fix it by removing the spinlock and relying on the
TG3_FLAG_INIT_COMPLETE flag to prevent race conditions between
tg3_get_stats64() and tg3_free_consistent().  TG3_FLAG_INIT_COMPLETE
is always cleared under tp->lock before tg3_free_consistent()
and therefore tg3_get_stats64() can safely access tp->hw_stats
under tp->lock if TG3_FLAG_INIT_COMPLETE is set.

Fixes: f5992b72ebe0 ("tg3: Fix race condition in tg3_get_stats64().")
Reported-by: Zumeng Chen <zumeng.c...@gmail.com>
Signed-off-by: Michael Chan <michael.c...@broadcom.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/net/ethernet/broadcom/tg3.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -8722,14 +8722,15 @@ static void tg3_free_consistent(struct t
        tg3_mem_rx_release(tp);
        tg3_mem_tx_release(tp);
 
-       /* Protect tg3_get_stats64() from reading freed tp->hw_stats. */
-       tg3_full_lock(tp, 0);
+       /* tp->hw_stats can be referenced safely:
+        *     1. under rtnl_lock
+        *     2. or under tp->lock if TG3_FLAG_INIT_COMPLETE is set.
+        */
        if (tp->hw_stats) {
                dma_free_coherent(&tp->pdev->dev, sizeof(struct tg3_hw_stats),
                                  tp->hw_stats, tp->stats_mapping);
                tp->hw_stats = NULL;
        }
-       tg3_full_unlock(tp);
 }
 
 /*
@@ -14163,7 +14164,7 @@ static struct rtnl_link_stats64 *tg3_get
        struct tg3 *tp = netdev_priv(dev);
 
        spin_lock_bh(&tp->lock);
-       if (!tp->hw_stats) {
+       if (!tp->hw_stats || !tg3_flag(tp, INIT_COMPLETE)) {
                *stats = tp->net_stats_prev;
                spin_unlock_bh(&tp->lock);
                return stats;