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-rw-r--r--drivers/block/zram/zram_drv.c15
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);