Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 143 insertions, 0 deletions

diff --git a/Documentation/networking/driver.rst b/Documentation/networking/driver.rst
new file mode 100644
index 000000000..920c0ec98
--- /dev/null
+++ b/Documentation/networking/driver.rst
@@ -0,0 +1,143 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+Softnet Driver Issues
+=====================
+
+Probing guidelines
+==================
+
+Address validation
+------------------
+
+Any hardware layer address you obtain for your device should
+be verified.  For example, for ethernet check it with
+linux/etherdevice.h:is_valid_ether_addr()
+
+Close/stop guidelines
+=====================
+
+Quiescence
+----------
+
+After the ndo_stop routine has been called, the hardware must
+not receive or transmit any data.  All in flight packets must
+be aborted. If necessary, poll or wait for completion of
+any reset commands.
+
+Auto-close
+----------
+
+The ndo_stop routine will be called by unregister_netdevice
+if device is still UP.
+
+Transmit path guidelines
+========================
+
+Stop queues in advance
+----------------------
+
+The ndo_start_xmit method must not return NETDEV_TX_BUSY under
+any normal circumstances.  It is considered a hard error unless
+there is no way your device can tell ahead of time when its
+transmit function will become busy.
+
+Instead it must maintain the queue properly.  For example,
+for a driver implementing scatter-gather this means:
+
+.. code-block:: c
+
+	static u32 drv_tx_avail(struct drv_ring *dr)
+	{
+		u32 used = READ_ONCE(dr->prod) - READ_ONCE(dr->cons);
+
+		return dr->tx_ring_size - (used & dr->tx_ring_mask);
+	}
+
+	static netdev_tx_t drv_hard_start_xmit(struct sk_buff *skb,
+					       struct net_device *dev)
+	{
+		struct drv *dp = netdev_priv(dev);
+		struct netdev_queue *txq;
+		struct drv_ring *dr;
+		int idx;
+
+		idx = skb_get_queue_mapping(skb);
+		dr = dp->tx_rings[idx];
+		txq = netdev_get_tx_queue(dev, idx);
+
+		//...
+		/* This should be a very rare race - log it. */
+		if (drv_tx_avail(dr) <= skb_shinfo(skb)->nr_frags + 1) {
+			netif_tx_stop_queue(txq);
+			netdev_warn(dev, "Tx Ring full when queue awake!\n");
+			return NETDEV_TX_BUSY;
+		}
+
+		//... queue packet to card ...
+
+		netdev_tx_sent_queue(txq, skb->len);
+
+		//... update tx producer index using WRITE_ONCE() ...
+
+		if (!netif_txq_maybe_stop(txq, drv_tx_avail(dr),
+					  MAX_SKB_FRAGS + 1, 2 * MAX_SKB_FRAGS))
+			dr->stats.stopped++;
+
+		//...
+		return NETDEV_TX_OK;
+	}
+
+And then at the end of your TX reclamation event handling:
+
+.. code-block:: c
+
+	//... update tx consumer index using WRITE_ONCE() ...
+
+	netif_txq_completed_wake(txq, cmpl_pkts, cmpl_bytes,
+				 drv_tx_avail(dr), 2 * MAX_SKB_FRAGS);
+
+Lockless queue stop / wake helper macros
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: include/net/netdev_queues.h
+   :doc: Lockless queue stopping / waking helpers.
+
+The standard macros like netif_txq_maybe_stop(), netif_txq_try_stop() etc.
+are well tested, prefer them over local synchronization schemes.
+
+No exclusive ownership
+----------------------
+
+An ndo_start_xmit method must not modify the shared parts of a
+cloned SKB.
+
+Timely completions
+------------------
+
+Do not forget that once you return NETDEV_TX_OK from your
+ndo_start_xmit method, it is your driver's responsibility to free
+up the SKB and in some finite amount of time.
+
+For example, this means that it is not allowed for your TX
+mitigation scheme to let TX packets "hang out" in the TX
+ring unreclaimed forever if no new TX packets are sent.
+This error can deadlock sockets waiting for send buffer room
+to be freed up.
+
+If you return NETDEV_TX_BUSY from the ndo_start_xmit method, you
+must not keep any reference to that SKB and you must not attempt
+to free it up.
+
+Error message reporting
+=======================
+
+A number of driver configuration interfaces pass a Netlink extended ACK
+(``extack``) object to the driver (either directly as an argument or
+as a member of a parameter struct). The drivers should try to report
+most errors via the ``extack`` object. System level exceptions,
+indicating that system or device is misbehaving or is in bad state,
+should continue to be reported to system logs.
+
+Messages should be passed **either** via ``extack`` **or** to system logs.
+Drivers should not try to report the same information to both.