iomap: Handle memory allocation failure in readahead

bio_alloc() can fail when we use GFP_NORETRY.  If it does, allocate
a bio large enough for a single page like mpage_readpages() does.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f080f54..56f2cca 100644 (file)
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -302,6 +302,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 
        if (!ctx->bio || !is_contig || bio_full(ctx->bio, plen)) {
                gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
+               gfp_t orig_gfp = gfp;
                int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
 
                if (ctx->bio)
@@ -310,6 +311,13 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
                if (ctx->is_readahead) /* same as readahead_gfp_mask */
                        gfp |= __GFP_NORETRY | __GFP_NOWARN;
                ctx->bio = bio_alloc(gfp, min(BIO_MAX_PAGES, nr_vecs));
+               /*
+                * If the bio_alloc fails, try it again for a single page to
+                * avoid having to deal with partial page reads.  This emulates
+                * what do_mpage_readpage does.
+                */
+               if (!ctx->bio)
+                       ctx->bio = bio_alloc(orig_gfp, 1);
                ctx->bio->bi_opf = REQ_OP_READ;
                if (ctx->is_readahead)
                        ctx->bio->bi_opf |= REQ_RAHEAD;