[PATCH net] net/mlx5: Fix double unregister of HCA_PORTS component

[Gerd Bayer <gbayer@linux.ibm.com>]

Clear hca_devcom_comp in device's private data after unregistering it in
LAG teardown. Otherwise a slightly lagging second pass through
mlx5_unload_one() might try to unregister it again and trip over
use-after-free.

On s390 almost all PCI level recovery events trigger two passes through
mxl5_unload_one() - one through the poll_health() method and one through
mlx5_pci_err_detected() as callback from generic PCI error recovery.
While testing PCI error recovery paths with more kernel debug features
enabled, this issue reproducibly led to kernel panics with the following
call chain:

 Unable to handle kernel pointer dereference in virtual kernel address space
 Failing address: 6b6b6b6b6b6b6000 TEID: 6b6b6b6b6b6b6803 ESOP-2 FSI
 Fault in home space mode while using kernel ASCE.
 AS:00000000705c4007 R3:0000000000000024
 Oops: 0038 ilc:3 [#1]SMP

 CPU: 14 UID: 0 PID: 156 Comm: kmcheck Kdump: loaded Not tainted
      6.18.0-20251130.rc7.git0.16131a59cab1.300.fc43.s390x+debug #1 PREEMPT

 Krnl PSW : 0404e00180000000 0000020fc86aa1dc (__lock_acquire+0x5c/0x15f0)
            R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
 Krnl GPRS: 0000000000000000 0000020f00000001 6b6b6b6b6b6b6c33 0000000000000000
            0000000000000000 0000000000000000 0000000000000001 0000000000000000
            0000000000000000 0000020fca28b820 0000000000000000 0000010a1ced8100
            0000010a1ced8100 0000020fc9775068 0000018fce14f8b8 0000018fce14f7f8
 Krnl Code: 0000020fc86aa1cc: e3b003400004        lg      %r11,832
            0000020fc86aa1d2: a7840211           brc     8,0000020fc86aa5f4
           *0000020fc86aa1d6: c09000df0b25       larl    %r9,0000020fca28b820
           >0000020fc86aa1dc: d50790002000       clc     0(8,%r9),0(%r2)
            0000020fc86aa1e2: a7840209           brc     8,0000020fc86aa5f4
            0000020fc86aa1e6: c0e001100401       larl    %r14,0000020fca8aa9e8
            0000020fc86aa1ec: c01000e25a00       larl    %r1,0000020fca2f55ec
            0000020fc86aa1f2: a7eb00e8           aghi    %r14,232

 Call Trace:
  __lock_acquire+0x5c/0x15f0
  lock_acquire.part.0+0xf8/0x270
  lock_acquire+0xb0/0x1b0
  down_write+0x5a/0x250
  mlx5_detach_device+0x42/0x110 [mlx5_core]
  mlx5_unload_one_devl_locked+0x50/0xc0 [mlx5_core]
  mlx5_unload_one+0x42/0x60 [mlx5_core]
  mlx5_pci_err_detected+0x94/0x150 [mlx5_core]
  zpci_event_attempt_error_recovery+0xcc/0x388

Fixes: 5a977b5833b7 ("net/mlx5: Lag, move devcom registration to LAG layer")
Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
---
Hi Shay et al,

while checking for potential regressions by Lukas Wunner's recent work
on pci_save/restore_state() for the recoverability of mlx5 functions I
consistently hit this bug. (Bjorn has queued this up for 6.19, according
to [0] and [1]) 

Apparently, the issue is unrelated to Lukas' work but can be reproduced
with master. It appears to be timing-sensitive, since it shows up only
when I use s390's debug_defconfig, but I think needs fixing anyhow, as
timing can change for other reasons, too.

I've spotted two additional places where the devcom reference is not
cleared after calling mlx5_devcom_unregister_component() in
drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c that I have not
addressed with a patch, since I'm unclear about how to test these
paths.

Thanks,
Gerd

[0] https://lore.kernel.org/all/cover.1760274044.git.lukas@wunner.de/
[1] https://lore.kernel.org/linux-pci/cover.1763483367.git.lukas@wunner.de/
---
 drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c b/drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c
index 3db0387bf6dcb727a65df9d0253f242554af06db..8ec04a5f434dd4f717d6d556649fcc2a584db847 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c
@@ -1413,6 +1413,7 @@ static int __mlx5_lag_dev_add_mdev(struct mlx5_core_dev *dev)
 static void mlx5_lag_unregister_hca_devcom_comp(struct mlx5_core_dev *dev)
 {
 	mlx5_devcom_unregister_component(dev->priv.hca_devcom_comp);
+	dev->priv.hca_devcom_comp = NULL;
 }
 
 static int mlx5_lag_register_hca_devcom_comp(struct mlx5_core_dev *dev)

---
base-commit: 4a26e7032d7d57c998598c08a034872d6f0d3945
change-id: 20251202-fix_lag-6a59b39a0b3c

Best regards,
-- 
Gerd Bayer <gbayer@linux.ibm.com>