[SRU][Bionic][PATCH 2/4] scsi: cxlflash: Synchronize reset and remove ops

[Joseph Salisbury]

From: Uma Krishnan <ukrishn at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1768431

The following Oops can be encountered if a device removal or system shutdown
is initiated while an EEH recovery is in process:

[c000000ff2f479c0] c008000015256f18 cxlflash_pci_slot_reset+0xa0/0x100
                                      [cxlflash]
[c000000ff2f47a30] c00800000dae22e0 cxl_pci_slot_reset+0x168/0x290 [cxl]
[c000000ff2f47ae0] c00000000003ef1c eeh_report_reset+0xec/0x170
[c000000ff2f47b20] c00000000003d0b8 eeh_pe_dev_traverse+0x98/0x170
[c000000ff2f47bb0] c00000000003f80c eeh_handle_normal_event+0x56c/0x580
[c000000ff2f47c60] c00000000003fba4 eeh_handle_event+0x2a4/0x338
[c000000ff2f47d10] c0000000000400b8 eeh_event_handler+0x1f8/0x200
[c000000ff2f47dc0] c00000000013da48 kthread+0x1a8/0x1b0
[c000000ff2f47e30] c00000000000b528 ret_from_kernel_thread+0x5c/0xb4

The remove handler frees AFU memory while the EEH recovery is in progress,
leading to a race condition. This can result in a crash if the recovery thread
tries to access this memory.

To resolve this issue, the cxlflash remove handler will evaluate the device
state and yield to any active reset or probing threads.

Signed-off-by: Uma Krishnan <ukrishn at linux.vnet.ibm.com>
Acked-by: Matthew R. Ochs <mrochs at linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
(cherry picked from linux-next commit a3feb6ef50def7c91244d7bd15a3625b7b49b81f)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
---
 drivers/scsi/cxlflash/main.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/cxlflash/main.c b/drivers/scsi/cxlflash/main.c
index 42a95b762bc0..dfe76485aab6 100644
--- a/drivers/scsi/cxlflash/main.c
+++ b/drivers/scsi/cxlflash/main.c
@@ -946,9 +946,9 @@ static void cxlflash_remove(struct pci_dev *pdev)
 		return;
 	}
 
-	/* If a Task Management Function is active, wait for it to complete
-	 * before continuing with remove.
-	 */
+	/* Yield to running recovery threads before continuing with remove */
+	wait_event(cfg->reset_waitq, cfg->state != STATE_RESET &&
+				     cfg->state != STATE_PROBING);
 	spin_lock_irqsave(&cfg->tmf_slock, lock_flags);
 	if (cfg->tmf_active)
 		wait_event_interruptible_lock_irq(cfg->tmf_waitq,
-- 
2.17.0