[PATCH net-next 04/17] sfc: Assert filter_sem write locked when required

[Edward Cree]

Based on a patch by Andrew Rybchenko <andrew.rybche...@oktetlabs.ru>

Signed-off-by: Edward Cree <ec...@solarflare.com>
---
 drivers/net/ethernet/sfc/ef10.c | 16 +++++++++++++++-
 drivers/net/ethernet/sfc/efx.h  |  9 +++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
index ebe3549..66cc963 100644
--- a/drivers/net/ethernet/sfc/ef10.c
+++ b/drivers/net/ethernet/sfc/ef10.c
@@ -3735,6 +3735,12 @@ static int efx_ef10_filter_table_probe(struct efx_nic 
*efx)
        size_t outlen;
        int rc;
 
+       if (!efx_rwsem_assert_write_locked(&efx->filter_sem))
+               return -EINVAL;
+
+       if (efx->filter_state) /* already probed */
+               return 0;
+
        table = kzalloc(sizeof(*table), GFP_KERNEL);
        if (!table)
                return -ENOMEM;
@@ -3846,7 +3852,6 @@ static void efx_ef10_filter_table_restore(struct efx_nic 
*efx)
                nic_data->must_restore_filters = false;
 }
 
-/* Caller must hold efx->filter_sem for write */
 static void efx_ef10_filter_table_remove(struct efx_nic *efx)
 {
        struct efx_ef10_filter_table *table = efx->filter_state;
@@ -3856,6 +3861,15 @@ static void efx_ef10_filter_table_remove(struct efx_nic 
*efx)
        int rc;
 
        efx->filter_state = NULL;
+       /* If we were called without locking, then it's not safe to free
+        * the table as others might be using it.  So we just WARN, leak
+        * the memory, and potentially get an inconsistent filter table
+        * state.
+        * This should never actually happen.
+        */
+       if (!efx_rwsem_assert_write_locked(&efx->filter_sem))
+               return;
+
        if (!table)
                return;
 
diff --git a/drivers/net/ethernet/sfc/efx.h b/drivers/net/ethernet/sfc/efx.h
index 5e3f93f..c3ae739 100644
--- a/drivers/net/ethernet/sfc/efx.h
+++ b/drivers/net/ethernet/sfc/efx.h
@@ -274,4 +274,13 @@ static inline void efx_device_detach_sync(struct efx_nic 
*efx)
        netif_tx_unlock_bh(dev);
 }
 
+static inline bool efx_rwsem_assert_write_locked(struct rw_semaphore *sem)
+{
+       if (WARN_ON(down_read_trylock(sem))) {
+               up_read(sem);
+               return false;
+       }
+       return true;
+}
+
 #endif /* EFX_EFX_H */