Merge ra.kernel.org:/pub/scm/linux/kernel/git/davem/net

1 files changed, 14 insertions, 1 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 7436b2d27fa3..a390c6d4f72d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -298,7 +298,8 @@ static void reset_bdev(struct zram *zram)
 	zram->backing_dev = NULL;
 	zram->old_block_size = 0;
 	zram->bdev = NULL;
-
+	zram->disk->queue->backing_dev_info->capabilities |=
+				BDI_CAP_SYNCHRONOUS_IO;
 	kvfree(zram->bitmap);
 	zram->bitmap = NULL;
 }
@@ -400,6 +401,18 @@ static ssize_t backing_dev_store(struct device *dev,
 	zram->backing_dev = backing_dev;
 	zram->bitmap = bitmap;
 	zram->nr_pages = nr_pages;
+	/*
+	 * With writeback feature, zram does asynchronous IO so it's no longer
+	 * synchronous device so let's remove synchronous io flag. Othewise,
+	 * upper layer(e.g., swap) could wait IO completion rather than
+	 * (submit and return), which will cause system sluggish.
+	 * Furthermore, when the IO function returns(e.g., swap_readpage),
+	 * upper layer expects IO was done so it could deallocate the page
+	 * freely but in fact, IO is going on so finally could cause
+	 * use-after-free when the IO is really done.
+	 */
+	zram->disk->queue->backing_dev_info->capabilities &=
+			~BDI_CAP_SYNCHRONOUS_IO;
 	up_write(&zram->init_lock);
 
 	pr_info("setup backing device %s\n", file_name);