FAILED: patch "[PATCH] dm log writes: fix bug with too large bios" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Mikulas Patocka <[email protected]>
Date: Tue, 30 Aug 2016 16:20:55 -0400
Subject: [PATCH] dm log writes: fix bug with too large bios

bio_alloc() can allocate a bio with at most BIO_MAX_PAGES (256) vector entries. However, the incoming bio may have more vector entries if it was allocated by other means. For example, bcache submits bios with more than BIO_MAX_PAGES entries. This results in bio_alloc() failure.

To avoid the failure, change the code so that it allocates bio with at most BIO_MAX_PAGES entries. If the incoming bio has more entries, bio_add_page() will fail and a new bio will be allocated - the code that handles bio_add_page() failure already exists in the dm-log-writes target.

index 4cc78aef9007..ba24f4f37efc 100644
@@ -260,7 +260,7 @@ static int log_one_block(struct log_writes_c *lc,
 	sector++;
 
 	atomic_inc(&lc->io_blocks);
-	bio = bio_alloc(GFP_KERNEL, block->vec_cnt);
+	bio = bio_alloc(GFP_KERNEL, min(block->vec_cnt, BIO_MAX_PAGES));
 	if (!bio) {
 		DMERR("Couldn't alloc log bio");
 		goto error;

@@ -282,7 +282,7 @@ static int log_one_block(struct log_writes_c *lc,
 		if (ret != block->vecs[i].bv_len) {
 			atomic_inc(&lc->io_blocks);
 			submit_bio(bio);
-			bio = bio_alloc(GFP_KERNEL, block->vec_cnt - i);
+			bio = bio_alloc(GFP_KERNEL, min(block->vec_cnt - i, BIO_MAX_PAGES));
 			if (!bio) {
 				DMERR("Couldn't alloc log bio");
 				goto error;