[PATCH] dmaengine: idxd: use spin_lock_irqsave before wait_event_lock_irq

[Rex Zhang <rex.zhang@xxxxxxxxx>]

In idxd_cmd_exec(), wait_event_lock_irq() explicitly calls
spin_unlock_irq()/spin_lock_irq(). If the interrupt is on before entering
wait_event_lock_irq(), it will become off status after
wait_event_lock_irq() is called. Later, wait_for_completion() may go to
sleep but irq is disabled. The scenario is warned in might_sleep().

Fix it by using spin_lock_irqsave() instead of the primitive spin_lock()
to save the irq status before entering wait_event_lock_irq() and using
spin_unlock_irqrestore() instead of the primitive spin_unlock() to restore
the irq status before entering wait_for_completion().

Before the change:
idxd_cmd_exec() {
interrupt is on
spin_lock()                        // interrupt is on
	wait_event_lock_irq()
		spin_unlock_irq()  // interrupt is enabled
		...
		spin_lock_irq()    // interrupt is disabled
spin_unlock()                      // interrupt is still disabled
wait_for_completion()              // report "BUG: sleeping function
				   // called from invalid context...
				   // in_atomic() irqs_disabled()"
}

After applying spin_lock_irqsave():
idxd_cmd_exec() {
interrupt is on
spin_lock_irqsave()                // save the on state
				   // interrupt is disabled
	wait_event_lock_irq()
		spin_unlock_irq()  // interrupt is enabled
		...
		spin_lock_irq()    // interrupt is disabled
spin_unlock_irqrestore()           // interrupt is restored to on
wait_for_completion()              // No Call trace
}

Fixes: f9f4082dbc56 ("dmaengine: idxd: remove interrupt disable for cmd_lock")
Signed-off-by: Rex Zhang <rex.zhang@xxxxxxxxx>
Signed-off-by: Lijun Pan <lijun.pan@xxxxxxxxx>
Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
Reviewed-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 drivers/dma/idxd/device.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
index 22d6f4e455b7..8f754f922217 100644
--- a/drivers/dma/idxd/device.c
+++ b/drivers/dma/idxd/device.c
@@ -477,6 +477,7 @@ static void idxd_cmd_exec(struct idxd_device *idxd, int cmd_code, u32 operand,
 	union idxd_command_reg cmd;
 	DECLARE_COMPLETION_ONSTACK(done);
 	u32 stat;
+	unsigned long flags;
 
 	if (idxd_device_is_halted(idxd)) {
 		dev_warn(&idxd->pdev->dev, "Device is HALTED!\n");
@@ -490,7 +491,7 @@ static void idxd_cmd_exec(struct idxd_device *idxd, int cmd_code, u32 operand,
 	cmd.operand = operand;
 	cmd.int_req = 1;
 
-	spin_lock(&idxd->cmd_lock);
+	spin_lock_irqsave(&idxd->cmd_lock, flags);
 	wait_event_lock_irq(idxd->cmd_waitq,
 			    !test_bit(IDXD_FLAG_CMD_RUNNING, &idxd->flags),
 			    idxd->cmd_lock);
@@ -507,7 +508,7 @@ static void idxd_cmd_exec(struct idxd_device *idxd, int cmd_code, u32 operand,
 	 * After command submitted, release lock and go to sleep until
 	 * the command completes via interrupt.
 	 */
-	spin_unlock(&idxd->cmd_lock);
+	spin_unlock_irqrestore(&idxd->cmd_lock, flags);
 	wait_for_completion(&done);
 	stat = ioread32(idxd->reg_base + IDXD_CMDSTS_OFFSET);
 	spin_lock(&idxd->cmd_lock);
-- 
2.25.1