Re: [PATCH 4/4] block: memory allocations in bounce_clone_bio must not fail

On Wed, Feb 24, 2021 at 05:12:36PM +0100, Christoph Hellwig wrote:

On Wed, Feb 24, 2021 at 07:19:52PM +0800, Ming Lei wrote:

quoted

quoted

 	if (bio_is_passthrough(bio_src))
-		bio = bio_kmalloc(GFP_NOIO, bio_segments(bio_src));
+		bio = bio_kmalloc(GFP_NOIO | __GFP_NOFAIL,
+				  bio_segments(bio_src));

bio_kmalloc() still may fail if bio_segments(bio_src) is > UIO_MAXIOV.

Yes, but bio_kmalloc is what is used to allocate the passthrough
requests to start with, so we'd not even make it here.

The original bio_kmalloc() may start with allowed nr_iovecs , but
later more pages are retrieved from iov_iter and added to the bio,
see bio_map_user_iov(). Then bounce_clone_bio() will see too big
bio_segments(bio_src) to be held in UIO_MAXIOV vecs.

This behavior is similar with blkdev_direct_IO().

-- 
Ming