[PATCH] ide-scsi: kmap scatter/gather before doing PIO

From: Stuart Hayes <Stuart_Hayes@dell.com>

The system can panic with a null pointer dereference using ide-scsi if
PIO is being done on scatter gather pages that are in high memory,
because page_address() returns 0.  We are actually seeing this using a
tape drive.  This patch will kmap_atomic() the pages before performing
PIO.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@elka.pw.edu.pl>

drivers/scsi/ide-scsi.c

@@ -179,8 +179,18 @@ static void idescsi_input_buffers (ide_drive_t *drive, idescsi_pc_t *pc, unsigne
 			return;
 		}
 		count = min(pc->sg->length - pc->b_count, bcount);
-		buf = page_address(pc->sg->page) + pc->sg->offset;
-		drive->hwif->atapi_input_bytes(drive, buf + pc->b_count, count);
+		if (PageHighMem(pc->sg->page)) {
+			unsigned long flags;
+
+			local_irq_save(flags);
+			buf = kmap_atomic(pc->sg->page, KM_IRQ0) + pc->sg->offset;
+			drive->hwif->atapi_input_bytes(drive, buf + pc->b_count, count);
+			kunmap_atomic(buf - pc->sg->offset, KM_IRQ0);
+			local_irq_restore(flags);
+		} else {
+			buf = page_address(pc->sg->page) + pc->sg->offset;
+			drive->hwif->atapi_input_bytes(drive, buf + pc->b_count, count);
+		}
 		bcount -= count; pc->b_count += count;
 		if (pc->b_count == pc->sg->length) {
 			pc->sg++;
@@ -201,8 +211,18 @@ static void idescsi_output_buffers (ide_drive_t *drive, idescsi_pc_t *pc, unsign
 			return;
 		}
 		count = min(pc->sg->length - pc->b_count, bcount);
-		buf = page_address(pc->sg->page) + pc->sg->offset;
-		drive->hwif->atapi_output_bytes(drive, buf + pc->b_count, count);
+		if (PageHighMem(pc->sg->page)) {
+			unsigned long flags;
+
+			local_irq_save(flags);
+			buf = kmap_atomic(pc->sg->page, KM_IRQ0) + pc->sg->offset;
+			drive->hwif->atapi_output_bytes(drive, buf + pc->b_count, count);
+			kunmap_atomic(buf - pc->sg->offset, KM_IRQ0);
+			local_irq_restore(flags);
+		} else {
+			buf = page_address(pc->sg->page) + pc->sg->offset;
+			drive->hwif->atapi_output_bytes(drive, buf + pc->b_count, count);
+		}
 		bcount -= count; pc->b_count += count;
 		if (pc->b_count == pc->sg->length) {
 			pc->sg++;