[PATCH iwl-net v2 0/2] i40e: fix set_ringparam error path crashes

[Aleksandr Loktionov <aleksandr.loktionov@intel.com>]

i40e_set_ringparam() has two independent ways to crash a live queue
while resizing descriptors. Both need a failure injected into the
middle of the resize to hit, but both are 100% reliable once you know
where.

Patch 1 is the reported bug: the free_tx: label frees vsi->tx_rings[i]
(the live, NAPI-active ring) instead of &tx_rings[i] (the staged copy),
on Rx allocation failure. desc/tx_bi go to NULL under a running NAPI,
next poll dereferences them. Reproduced by forcing an Rx alloc failure
right after a Tx descriptor count change; panic address matched the
original report exactly (CR2 == old_count * sizeof(desc)).

Patch 2 was found reviewing patch 1. The staged tx_rings[] copies are
shallow copies of the live rings, so they carry over the same
ring->netdev/queue_index. Freeing one of these copies before
i40e_down() has run - either from this same free_tx: label or from the
i40e_setup_tx_descriptors() failure unwind loop above it - resets BQL
state for the live queue it was copied from. dql_completed() then
BUG_ONs the next time the live ring reports a completion that was
queued before the reset. This one predates patch 1's bug by four
years (Fixes: 9f65e15b4f98, 2013) and doesn't need patch 1 applied to
be reachable via the setup_tx_descriptors() path.

Reproduced by forcing i40e_setup_tx_descriptors() to fail on a later
queue while flooding real Tx traffic on the earlier ones:

  kernel BUG at lib/dynamic_queue_limits.c:99!
  RIP: dql_completed+0x285/0x2a0
  Call Trace:
   <IRQ>
   i40e_napi_poll+0x74b/0x1700 [i40e]
   __napi_poll+0x10a/0x200
   net_rx_action+0x2f7/0x380
   handle_softirqs+0xcc/0x270

Confirmed clean with the fix applied, same traffic, repeated
resize cycles.

Patch 2 touches both error paths above, but only the free_tx: hunk
needs patch 1 applied first to match its diff context - the
setup_tx_descriptors() unwind hunk applies, and matters, on its own.

Cc: Simon Horman <horms@kernel.org>

Aleksandr Loktionov (2):
  i40e: fix set_ringparam error path freeing live Tx rings
  i40e: avoid resetting BQL state when freeing temporary Tx rings in
    set_ringparam

 drivers/net/ethernet/intel/i40e/i40e_ethtool.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

-- 
2.52.0