Patch "i40e: avoid NULL pointer dereference and recursive errors on early PCI error" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

i40e: avoid NULL pointer dereference and recursive errors on early PCI error

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
i40e-avoid-null-pointer-dereference-and-recursive-errors-on-early-pci-error.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Guilherme G Piccoli <[email protected]>
Date: Mon, 3 Oct 2016 00:31:12 -0700
Subject: i40e: avoid NULL pointer dereference and recursive errors on early PCI error

From: Guilherme G Piccoli <[email protected]>

commit edfc23ee3e0ebbb6713d7574ab1b00abff178f6c upstream.

Although rare, it's possible to hit PCI error early on device probe, meaning possibly some structs are not entirely initialized, and some might even be completely uninitialized, leading to NULL pointer dereference.

The i40e driver currently presents a "bad" behavior if device hits such early PCI error: firstly, the struct i40e_pf might not be attached to pci_dev yet, leading to a NULL pointer dereference on access to pf->state.

Even checking if the struct is NULL and avoiding the access in that case isn't enough, since the driver cannot recover from PCI error that early; in our experiments we saw multiple failures on kernel log, like:

  [549.664] i40e 0007:01:00.1: Initial pf_reset failed: -15
  [549.664] i40e: probe of 0007:01:00.1 failed with error -15
  [...]
  [871.644] i40e 0007:01:00.1: The driver for the device stopped because the
  device firmware failed to init. Try updating your NVM image.
  [871.644] i40e: probe of 0007:01:00.1 failed with error -32
  [...]
  [872.516] i40e 0007:01:00.0: ARQ: Unknown event 0x0000 ignored

Between the first probe failure (error -15) and the second (error -32) another PCI error happened due to the first bad probe. Also, driver started to flood console with those ARQ event messages.

This patch will prevent these issues by allowing error recovery mechanism to remove the failed device from the system instead of trying to recover from early PCI errors during device probe.

---
 drivers/net/ethernet/intel/i40e/i40e_main.c |    6 ++++++
 1 file changed, 6 insertions(+)

@@ -10853,6 +10853,12 @@ static pci_ers_result_t i40e_pci_error_d
 
 	dev_info(&pdev->dev, "%s: error %d\n", __func__, error);
 
+	if (!pf) {
+		dev_info(&pdev->dev,
+			 "Cannot recover - error happened during device probe\n");
+		return PCI_ERS_RESULT_DISCONNECT;
+	}
+
 	/* shutdown all operations */
 	if (!test_bit(__I40E_SUSPENDED, &pf->state)) {
 		rtnl_lock();

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/i40e-avoid-null-pointer-dereference-and-recursive-errors-on-early-pci-error.patch