[PATCH net v2] bnxt_en: Take RTNL before netif_close() when aborting FW reset

[Bryan Cochrane <bcochrane@google.com>]

netif_close() must be called with RTNL held in addition to the netdev
instance lock: __dev_close_many() asserts it, and the NETDEV_GOING_DOWN
and NETDEV_DOWN notifier chains it runs rely on it for serialization.

Commit 004b5008016a ("eth: bnxt: remove most dependencies on RTNL")
replaced rtnl_lock() with netdev_lock() in bnxt_fw_reset_task() and
bnxt_fw_reset(). That is sufficient for the paths that only tear the
NIC down internally with __bnxt_close_nic(), but the abort paths close
the netdev via bnxt_fw_reset_abort() -> netif_close(), and the error
path in bnxt_fw_reset() calls netif_close() directly. Those now run
without RTNL and trigger a WARN_ONCE() cascade when a firmware reset is
aborted:

  RTNL: assertion failed at net/core/dev.c (1740)
  WARNING: net/core/dev.c:1740 at __dev_close_many+0x1be/0x1f0
  Workqueue: bnxt_pf_wq bnxt_fw_reset_task [bnxt_en]
  Call Trace:
   netif_close_many+0xb5/0x190
   netif_close+0xa2/0xd0
   bnxt_fw_reset_task.cold+0x8d/0x213 [bnxt_en]
   process_one_work+0x19d/0x3a0
   worker_thread+0x1af/0x320
   kthread+0xe3/0x120

followed by the same assertion from call_netdevice_notifiers_info(),
fib_rules_event(), inetdev_event(), rtnl_fill_ifinfo(),
devlink_compat_phys_port_name_get() and ip_mc_down().

This was observed on a machine in real use with a BCM57504 (4 PFs,
FW 236.1.153.0) running v7.1.6: the firmware crashed, announced a
"Fatal firmware reset event" and then failed to come back within the
advertised max wait, so bnxt_fw_reset_task() aborted the reset on all
ports:

  bnxt_en 0000:c1:00.1 eno16905np1: Firmware reset aborted
  bnxt_en 0000:c1:00.1 eno16905np1: fw_health_status 0x448100

Take RTNL (before the netdev instance lock, matching the OPENING state
which already uses rtnl_trylock()) in the fw_reset_abort path of
bnxt_fw_reset_task() and route the POLL_VF abort through that same
path.

In bnxt_fw_reset() only the error path that closes the device after
bnxt_get_registered_vfs() fails needs RTNL: drop the instance lock,
take RTNL and the instance lock, then clear BNXT_STATE_IN_FW_RESET and
close. The normal reset flow, which may run on many VFs at the same
time, keeps running without RTNL. BNXT_STATE_IN_FW_RESET stays set
across the lock switch, so a concurrent close marks the reset aborted
as it does today and a concurrent recovery request backs off.

The bug was found by inspecting the kernel log of the affected machine
and the driver source; the fix was prepared with the help of an AI
coding assistant (Gemini based) and reviewed by the submitter. It is
build tested (allmodconfig with W=1, plus the same change on top of
v7.1.6 built as a module for the affected BCM57504 host). The aborted
reset path itself only runs when the firmware fails to return from a
reset, which could not be reproduced on demand.

Fixes: 004b5008016a ("eth: bnxt: remove most dependencies on RTNL")
Cc: stable@vger.kernel.org
Signed-off-by: Bryan Cochrane <bcochrane@google.com>
---
v2:
 - Keep bnxt_lock_sp() in bnxt_fw_reset() and take RTNL only on the
   bnxt_get_registered_vfs() error path, so that the normal FW reset
   flow does not add RTNL contention when many VFs recover at the same
   time (Michael Chan).
 - Dropped Stanislav's Acked-by because of the change above.
v1: https://lore.kernel.org/netdev/20261029032832.1511180-1-bcochrane@google.com/
 drivers/net/ethernet/broadcom/bnxt/bnxt.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
index 33c4cacc8ffe..1ea1e8266eab 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
@@ -14860,9 +14860,16 @@ void bnxt_fw_reset(struct bnxt *bp)
 		if (n < 0) {
 			netdev_err(bp->dev, "Firmware reset aborted, rc = %d\n",
 				   n);
+			/* netif_close() requires RTNL, which must be taken
+			 * before the netdev instance lock.
+			 */
+			netdev_unlock(bp->dev);
+			rtnl_lock();
+			netdev_lock(bp->dev);
 			clear_bit(BNXT_STATE_IN_FW_RESET, &bp->state);
 			netif_close(bp->dev);
-			goto fw_reset_exit;
+			bnxt_rtnl_unlock_sp(bp);
+			return;
 		} else if (n > 0) {
 			u16 vf_tmo_dsecs = n * 10;
 
@@ -15547,9 +15554,8 @@ static void bnxt_fw_reset_task(struct work_struct *work)
 		bp->fw_reset_timestamp = jiffies;
 		netdev_lock(bp->dev);
 		if (test_bit(BNXT_STATE_ABORT_ERR, &bp->state)) {
-			bnxt_fw_reset_abort(bp, rc);
 			netdev_unlock(bp->dev);
-			goto ulp_start;
+			goto fw_reset_abort;
 		}
 		bnxt_fw_reset_close(bp);
 		if (bp->fw_cap & BNXT_FW_CAP_ERR_RECOVER_RELOAD) {
@@ -15682,9 +15688,11 @@ static void bnxt_fw_reset_task(struct work_struct *work)
 		netdev_err(bp->dev, "fw_health_status 0x%x\n", sts);
 	}
 fw_reset_abort:
+	rtnl_lock();
 	netdev_lock(bp->dev);
 	bnxt_fw_reset_abort(bp, rc);
 	netdev_unlock(bp->dev);
+	rtnl_unlock();
 ulp_start:
 	if (!rc)
 		bnxt_ulp_start(bp);

base-commit: c3e67bd82b9b9b1a5118f09a429ccefe2aab0741
-- 
2.56.0.385.gac671c819a-goog