y testing a pair of tasks was reported to be hung:

[10144.859042] mlx5_core 0000:00:00.1: mlx5_health_try_recover:338:(pid 5553): health recovery flow aborted, PCI reads still not working
[10320.359160] INFO: task kmcheck:72 blocked for more than 122 seconds.
[10320.359169]       Not tainted 5.14.0-570.12.1.bringup7.el9.s390x #1
[10320.359171] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[10320.359172] task:kmcheck         state:D stack:0     pid:72    tgid:72    ppid:2      flags:0x00000000
[10320.359176] Call Trace:
[10320.359178]  [<000000065256f030>] __schedule+0x2a0/0x590
[10320.359187]  [<000000065256f356>] schedule+0x36/0xe0
[10320.359189]  [<000000065256f572>] schedule_preempt_disabled+0x22/0x30
[10320.359192]  [<0000000652570a94>] __mutex_lock.constprop.0+0x484/0x8a8
[10320.359194]  [<000003ff800673a4>] mlx5_unload_one+0x34/0x58 [mlx5_core]
[10320.359360]  [<000003ff8006745c>] mlx5_pci_err_detected+0x94/0x140 [mlx5_core]
[10320.359400]  [<0000000652556c5a>] zpci_event_attempt_error_recovery+0xf2/0x398
[10320.359406]  [<0000000651b9184a>] __zpci_event_error+0x23a/0x2c0
[10320.359411]  [<00000006522b3958>] chsc_process_event_information.constprop.0+0x1c8/0x1e8
[10320.359416]  [<00000006522baf1a>] crw_collect_info+0x272/0x338
[10320.359418]  [<0000000651bc9de0>] kthread+0x108/0x110
[10320.359422]  [<0000000651b42ea4>] __ret_from_fork+0x3c/0x58
[10320.359425]  [<0000000652576642>] ret_from_fork+0xa/0x30
[10320.359440] INFO: task kworker/u1664:6:1514 blocked for more than 122 seconds.
[10320.359441]       Not tainted 5.14.0-570.12.1.bringup7.el9.s390x #1
[10320.359442] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[10320.359443] task:kworker/u1664:6 state:D stack:0     pid:1514  tgid:1514  ppid:2      flags:0x00000000
[10320.359447] Workqueue: mlx5_health0000:00:00.0 mlx5_fw_fatal_reporter_err_work [mlx5_core]
[10320.359492] Call Trace:
[10320.359521]  [<000000065256f030>] __schedule+0x2a0/0x590
[10320.359524]  [<000000065256f356>] schedule+0x36/0xe0
[10320.359526]  [<0000000652172e28>] pci_wait_cfg+0x80/0xe8
[10320.359532]  [<0000000652172f94>] pci_cfg_access_lock+0x74/0x88
[10320.359534]  [<000003ff800916b6>] mlx5_vsc_gw_lock+0x36/0x178 [mlx5_core]
[10320.359585]  [<000003ff80098824>] mlx5_crdump_collect+0x34/0x1c8 [mlx5_core]
[10320.359637]  [<000003ff80074b62>] mlx5_fw_fatal_reporter_dump+0x6a/0xe8 [mlx5_core]
[10320.359680]  [<0000000652512242>] devlink_health_do_dump.part.0+0x82/0x168
[10320.359683]  [<0000000652513212>] devlink_health_report+0x19a/0x230
[10320.359685]  [<000003ff80075a12>] mlx5_fw_fatal_reporter_err_work+0xba/0x1b0 [mlx5_core]
[10320.359728]  [<0000000651bbf852>] process_one_work+0x1c2/0x458
[10320.359733]  [<0000000651bc073e>] worker_thread+0x3ce/0x528
[10320.359735]  [<0000000651bc9de0>] kthread+0x108/0x110
[10320.359737]  [<0000000651b42ea4>] __ret_from_fork+0x3c/0x58
[10320.359739]  [<0000000652576642>] ret_from_fork+0xa/0x30

No kernel log of the exact same error with an upstream kernel is
available - but the very same deadlock situation can be constructed there,
too:

- task: kmcheck
  mlx5_unload_one() tries to acquire devlink lock while the PCI error
  recovery code has set pdev->block_cfg_access by way of
  pci_cfg_access_lock()
- task: kworker
  mlx5_crdump_collect() tries to set block_cfg_access through
  pci_cfg_access_lock() while devlink_health_report() had acquired
  the devlink lock.

A similar deadlock situation can be reproduced by requesting a
crdump with
  > devlink health dump show pci/<BDF> reporter fw_fatal

while PCI error recovery is executed on the same <BDF> physical function
by mlx5_core's pci_error_handlers. On s390 this can be injected with
  > zpcictl --reset-fw <BDF>

Extensive tests with the same setup that showed the original dead-lock
didn't reproduce, nor did the second deadlock situation hit with
this patch applied.

Fixes: b25bbc2f24dc ("net/mlx5: Add Vendor Specific Capability access gateway")
Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>

---

v1:
Attempted to fix this differently, but still had potential for deadlocks
and the second inject reproduced it quite regularly, still
https://lore.kernel.org/netdev/20250807131130.4056349-1-gbayer@linux.ibm.com/
---
 drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c
index 432c98f2626d..f668237b6bb0 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c
@@ -73,7 +73,9 @@ int mlx5_vsc_gw_lock(struct mlx5_core_dev *dev)
 	u32 lock_val;
 	int ret;
 
-	pci_cfg_access_lock(dev->pdev);
+	if (!pci_cfg_access_trylock(dev->pdev))
+		return -EBUSY;
+
 	do {
 		if (retries > VSC_MAX_RETRIES) {
 			ret = -EBUSY;
-- 
2.48.1[PATCH net v2] net/mlx5: Avoid deadlock between PCI error recovery and health reporterGerd Bayer <gbayer@linux.ibm.com> undefinedTariq Toukan <tariqt@nvidia.com>, Saeed Mahameed <saeedm@nvidia.com>, Leon Romanovsky <leon@kernel.org>, Shay Drori <shayd@nvidia.com>, Mark Bloch <mbloch@nvidia.com> undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefinedƒLƒ…c
