soc: aspeed: espi-slave: Avoid calling put_user in atomic context

put_user() can sleep, which means that calling it in atomic context can
cause deadlock.
aspeed-espi-slave is calling it under spin_lock_irqsave(), resulting in
the following lockdep splat:
[   18.796723] BUG: sleeping function called from invalid context at drivers/soc/aspeed/aspeed-espi-slave.c:309
[   18.807742] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 311, name: host-misc-manag
[   18.817486] INFO: lockdep is turned off.
[   18.821869] irq event stamp: 0
[   18.825289] hardirqs last  enabled at (0): [<00000000>] 0x0
[   18.831551] hardirqs last disabled at (0): [<8011ed40>] copy_process+0x7b0/0x1be8
[   18.839941] softirqs last  enabled at (0): [<8011ed40>] copy_process+0x7b0/0x1be8
[   18.848308] softirqs last disabled at (0): [<00000000>] 0x0
[   18.854538] CPU: 0 PID: 311 Comm: host-misc-manag Not tainted 5.15.0-14fcc87-dirty-7b64388 openbmc#1
[   18.864070] Hardware name: Generic DT based system
[   18.869421] Backtrace:
[   18.872155] [<80a48ec4>] (dump_backtrace) from [<80a492a8>] (show_stack+0x20/0x24)
[   18.880638]  r7:0242c06c r6:00000080 r5:80cb88f4 r4:600d0093
[   18.886969] [<80a49288>] (show_stack) from [<80a5596c>] (dump_stack_lvl+0x60/0x78)
[   18.895440] [<80a5590c>] (dump_stack_lvl) from [<80a5599c>] (dump_stack+0x18/0x1c)
[   18.903907]  r7:0242c06c r6:00000135 r5:80d0a958 r4:8ffc2000
[   18.910226] [<80a55984>] (dump_stack) from [<80160d3c>] (___might_sleep+0x1b0/0x2c0)
[   18.918901] [<80160b8c>] (___might_sleep) from [<80160ebc>] (__might_sleep+0x70/0xac)
[   18.927818]  r6:00000000 r5:00000135 r4:80d0a958
[   18.933024] [<80160e4c>] (__might_sleep) from [<802a1cf8>] (__might_fault+0x48/0xb0)
[   18.941690]  r6:8238da58 r5:00000000 r4:ffffe000
[   18.946848] [<802a1cb0>] (__might_fault) from [<8060ed78>] (aspeed_espi_pltrstn_read+0xac/0x254)
[   18.956679]  r5:8238da80 r4:ffffe000
[   18.960669] [<8060eccc>] (aspeed_espi_pltrstn_read) from [<802d6024>] (vfs_read+0xc0/0x320)
[   18.970011]  r10:00000003 r9:8ffc2000 r8:8060eccc r7:00000001 r6:00000001 r5:8ffc3f68
[   18.978754]  r4:84eb48c0
[   18.981582] [<802d5f64>] (vfs_read) from [<802d6e04>] (ksys_read+0x70/0xf4)
[   18.989378]  r10:00000003 r9:8ffc2000 r8:80100224 r7:00000000 r6:00000000 r5:84eb48c0
[   18.998122]  r4:84eb48c0
[   19.000946] [<802d6d94>] (ksys_read) from [<802d6ea0>] (sys_read+0x18/0x1c)
[   19.008735]  r7:00000003 r6:7ec07a00 r5:76fc3070 r4:0242c220
[   19.015055] [<802d6e88>] (sys_read) from [<80100060>] (ret_fast_syscall+0x0/0x1c)
[   19.023419] Exception stack(0x8ffc3fa8 to 0x8ffc3ff0)
[   19.029063] 3fa0:                   0242c220 76fc3070 00000007 0242c06c 00000001 00000000
[   19.038196] 3fc0: 0242c220 76fc3070 7ec07a00 00000003 0242c23c 0242c06c 00000001 00000000
[   19.047330] 3fe0: 00446be4 7ec079d8 00424b88 76cb536c

Rearrange the code to avoid calling *_user() function under spin_lock.
Also, use the regular *_irq() variant instead if *_irqsave(), since
it's only used for serializing process context with IRQ handler.

Signed-off-by: Iwona Winiarska <iwona.winiarska@intel.com>
Change-Id: Iaf17ddd17c020c8ee8c60c2fc98a57b97133e7a6

drivers/soc/aspeed/aspeed-espi-slave.c

@@ -294,24 +294,17 @@ static ssize_t aspeed_espi_pltrstn_read(struct file *filp, char __user *buf,
 {
 	struct aspeed_espi *priv = to_aspeed_espi(filp);
 	DECLARE_WAITQUEUE(wait, current);
-	unsigned long flags;
-	char old_sample;
+	char data, old_sample;
 	int ret = 0;
 
-	spin_lock_irqsave(&priv->pltrstn_lock, flags);
+	spin_lock_irq(&priv->pltrstn_lock);
 
 	if (filp->f_flags & O_NONBLOCK) {
 		if (!priv->pltrstn_in_avail) {
 			ret = -EAGAIN;
 			goto out_unlock;
 		}
-		char data = priv->pltrstn;
-		ret = put_user(data, (unsigned long __user *)buf);
-		if (!ret){
-			ret = sizeof(data);
-		} else{
-			ret = -EAGAIN;
-		}
+		data = priv->pltrstn;
 		priv->pltrstn_in_avail = false;
 	} else {
 		add_wait_queue(&priv->pltrstn_waitq, &wait);
@@ -320,30 +313,33 @@ static ssize_t aspeed_espi_pltrstn_read(struct file *filp, char __user *buf,
 		old_sample = priv->pltrstn;
 
 		do {
-			char new_sample = priv->pltrstn;
-
-			if (old_sample != new_sample) {
-				ret = put_user(new_sample,
-						 (unsigned long __user *)buf);
-				if (!ret)
-					ret = sizeof(new_sample);
-			} else if (signal_pending(current)) {
-				ret = -ERESTARTSYS;
+			if (old_sample != priv->pltrstn) {
+				data = priv->pltrstn;
+				priv->pltrstn_in_avail = false;
+				break;
 			}
 
-			if (!ret) {
-				spin_unlock_irqrestore(&priv->pltrstn_lock,
-							 flags);
+			if (signal_pending(current)) {
+				ret = -ERESTARTSYS;
+			} else {
+				spin_unlock_irq(&priv->pltrstn_lock);
 				schedule();
-				spin_lock_irqsave(&priv->pltrstn_lock, flags);
+				spin_lock_irq(&priv->pltrstn_lock);
 			}
 		} while (!ret);
 
 		remove_wait_queue(&priv->pltrstn_waitq, &wait);
 		set_current_state(TASK_RUNNING);
 	}
 out_unlock:
-	spin_unlock_irqrestore(&priv->pltrstn_lock, flags);
+	spin_unlock_irq(&priv->pltrstn_lock);
+
+	if (ret)
+		return ret;
+
+	ret = put_user(data, buf);
+	if (!ret)
+		ret = sizeof(data);
 
 	return ret;
 }