ata: libata-core: Fix ata_port_request_pm() locking

The function ata_port_request_pm() checks the port flag
ATA_PFLAG_PM_PENDING and calls ata_port_wait_eh() if this flag is set to
ensure that power management operations for a port are not scheduled
simultaneously. However, this flag check is done without holding the
port lock.

Fix this by taking the port lock on entry to the function and checking
the flag under this lock. The lock is released and re-taken if
ata_port_wait_eh() needs to be called. The two WARN_ON() macros checking
that the ATA_PFLAG_PM_PENDING flag was cleared are removed as the first
call is racy and the second one done without holding the port lock.

Fixes: 5ef4108 ("ata: add ata port system PM callbacks")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Tested-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>

Author: damien-lemoal

drivers/ata/libata-core.c

@@ -5037,17 +5037,19 @@ static void ata_port_request_pm(struct ata_port *ap, pm_message_t mesg,
 	struct ata_link *link;
 	unsigned long flags;
 
-	/* Previous resume operation might still be in
-	 * progress.  Wait for PM_PENDING to clear.
+	spin_lock_irqsave(ap->lock, flags);
+
+	/*
+	 * A previous PM operation might still be in progress. Wait for
+	 * ATA_PFLAG_PM_PENDING to clear.
 	 */
 	if (ap->pflags & ATA_PFLAG_PM_PENDING) {
+		spin_unlock_irqrestore(ap->lock, flags);
 		ata_port_wait_eh(ap);
-		WARN_ON(ap->pflags & ATA_PFLAG_PM_PENDING);
+		spin_lock_irqsave(ap->lock, flags);
 	}
 
-	/* request PM ops to EH */
-	spin_lock_irqsave(ap->lock, flags);
-
+	/* Request PM operation to EH */
 	ap->pm_mesg = mesg;
 	ap->pflags |= ATA_PFLAG_PM_PENDING;
 	ata_for_each_link(link, ap, HOST_FIRST) {
@@ -5059,10 +5061,8 @@ static void ata_port_request_pm(struct ata_port *ap, pm_message_t mesg,
 
 	spin_unlock_irqrestore(ap->lock, flags);
 
-	if (!async) {
+	if (!async)
 		ata_port_wait_eh(ap);
-		WARN_ON(ap->pflags & ATA_PFLAG_PM_PENDING);
-	}
 }
 
 /*