ata: libata: Fix ata_exec_internal()

Some but not all ata_exec_internal() calls happen from the context of
the ATA error handler. Commit c0c362b ("libata: implement cross-port
EH exclusion") added ata_eh_release() and ata_eh_acquire() calls in
ata_exec_internal(). Calling these functions is necessary if the caller
holds the eh_mutex but is not allowed if the caller doesn't hold that
mutex. Fix this by only calling ata_eh_release() and ata_eh_acquire() if
the caller holds the eh_mutex. An example of an indirect caller of
ata_exec_internal() that does not hold the eh_mutex is
ata_host_register().

Fixes: c0c362b ("libata: implement cross-port EH exclusion")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>

Author: bvanassche

drivers/ata/libata-core.c

@@ -1540,6 +1540,7 @@ unsigned int ata_exec_internal(struct ata_device *dev, struct ata_taskfile *tf,
 {
 	struct ata_link *link = dev->link;
 	struct ata_port *ap = link->ap;
+	const bool owns_eh_mutex = ap->host->eh_owner == current;
 	u8 command = tf->command;
 	struct ata_queued_cmd *qc;
 	struct scatterlist sgl;
@@ -1617,11 +1618,25 @@ unsigned int ata_exec_internal(struct ata_device *dev, struct ata_taskfile *tf,
 		}
 	}
 
-	ata_eh_release(ap);
+	if (owns_eh_mutex) {
+		/*
+		 * To prevent that the compiler complains about the
+		 * ata_eh_release() call below.
+		 */
+		__acquire(&ap->host->eh_mutex);
+		ata_eh_release(ap);
+	}
 
 	rc = wait_for_completion_timeout(&wait, msecs_to_jiffies(timeout));
 
-	ata_eh_acquire(ap);
+	if (owns_eh_mutex) {
+		ata_eh_acquire(ap);
+		/*
+		 * To prevent that the compiler complains about the above
+		 * ata_eh_acquire() call.
+		 */
+		__release(&ap->host->eh_mutex);
+	}
 
 	ata_sff_flush_pio_task(ap);