erofs: use workqueue decompression for atomic contexts only

z_erofs_decompressqueue_endio may not be executed in the atomic
context, for example, when dm-verity is turned on. In this scenario,
data can be decompressed directly to get rid of additional kworker
scheduling overhead.

Link: https://lore.kernel.org/r/20210317035448.13921-2-huangjianan@oppo.comReviewed-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

fs/erofs/zdata.c

@@ -706,6 +706,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 	goto out;
 }
 
+static void z_erofs_decompressqueue_work(struct work_struct *work);
 static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 				       bool sync, int bios)
 {
@@ -720,8 +721,14 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 		return;
 	}
 
-	if (!atomic_add_return(bios, &io->pending_bios))
+	if (atomic_add_return(bios, &io->pending_bios))
+		return;
+	/* Use workqueue decompression for atomic contexts only */
+	if (in_atomic() || irqs_disabled()) {
 		queue_work(z_erofs_workqueue, &io->u.work);
+		return;
+	}
+	z_erofs_decompressqueue_work(&io->u.work);
 }
 
 static bool z_erofs_page_is_invalidated(struct page *page)