ext4: bio_alloc with __GFP_DIRECT_RECLAIM never fails

Similar to [1] [2], bio_alloc with __GFP_DIRECT_RECLAIM flags
guarantees bio allocation under some given restrictions, as
stated in block/bio.c and fs/direct-io.c So here it's ok to
not check for NULL value from bio_alloc().

[1] https://lore.kernel.org/r/20191030035518.65477-1-gaoxiang25@huawei.com
[2] https://lore.kernel.org/r/20190830162812.GA10694@infradead.org
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20191031092315.139267-1-gaoxiang25@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 893913d..24aeedb 100644 (file)
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -394,14 +394,16 @@ void ext4_io_submit_init(struct ext4_io_submit *io,
        io->io_end = NULL;
 }
 
-static int io_submit_init_bio(struct ext4_io_submit *io,
-                             struct buffer_head *bh)
+static void io_submit_init_bio(struct ext4_io_submit *io,
+                              struct buffer_head *bh)
 {
        struct bio *bio;
 
+       /*
+        * bio_alloc will _always_ be able to allocate a bio if
+        * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
+        */
        bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES);
-       if (!bio)
-               return -ENOMEM;
        bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
        bio_set_dev(bio, bh->b_bdev);
        bio->bi_end_io = ext4_end_bio;
@@ -409,13 +411,12 @@ static int io_submit_init_bio(struct ext4_io_submit *io,
        io->io_bio = bio;
        io->io_next_block = bh->b_blocknr;
        wbc_init_bio(io->io_wbc, bio);
-       return 0;
 }
 
-static int io_submit_add_bh(struct ext4_io_submit *io,
-                           struct inode *inode,
-                           struct page *page,
-                           struct buffer_head *bh)
+static void io_submit_add_bh(struct ext4_io_submit *io,
+                            struct inode *inode,
+                            struct page *page,
+                            struct buffer_head *bh)
 {
        int ret;
 
@@ -424,9 +425,7 @@ submit_and_retry:
                ext4_io_submit(io);
        }
        if (io->io_bio == NULL) {
-               ret = io_submit_init_bio(io, bh);
-               if (ret)
-                       return ret;
+               io_submit_init_bio(io, bh);
                io->io_bio->bi_write_hint = inode->i_write_hint;
        }
        ret = bio_add_page(io->io_bio, page, bh->b_size, bh_offset(bh));
@@ -434,7 +433,6 @@ submit_and_retry:
                goto submit_and_retry;
        wbc_account_cgroup_owner(io->io_wbc, page, bh->b_size);
        io->io_next_block++;
-       return 0;
 }
 
 int ext4_bio_write_page(struct ext4_io_submit *io,
@@ -527,8 +525,14 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
                                gfp_flags |= __GFP_NOFAIL;
                                goto retry_encrypt;
                        }
-                       bounce_page = NULL;
-                       goto out;
+
+                       printk_ratelimited(KERN_ERR "%s: ret = %d\n", __func__, ret);
+                       redirty_page_for_writepage(wbc, page);
+                       do {
+                               clear_buffer_async_write(bh);
+                               bh = bh->b_this_page;
+                       } while (bh != head);
+                       goto unlock;
                }
        }
 
@@ -536,30 +540,13 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
        do {
                if (!buffer_async_write(bh))
                        continue;
-               ret = io_submit_add_bh(io, inode, bounce_page ?: page, bh);
-               if (ret) {
-                       /*
-                        * We only get here on ENOMEM.  Not much else
-                        * we can do but mark the page as dirty, and
-                        * better luck next time.
-                        */
-                       break;
-               }
+               io_submit_add_bh(io, inode,
+                                bounce_page ? bounce_page : page, bh);
                nr_submitted++;
                clear_buffer_dirty(bh);
        } while ((bh = bh->b_this_page) != head);
 
-       /* Error stopped previous loop? Clean up buffers... */
-       if (ret) {
-       out:
-               fscrypt_free_bounce_page(bounce_page);
-               printk_ratelimited(KERN_ERR "%s: ret = %d\n", __func__, ret);
-               redirty_page_for_writepage(wbc, page);
-               do {
-                       clear_buffer_async_write(bh);
-                       bh = bh->b_this_page;
-               } while (bh != head);
-       }
+unlock:
        unlock_page(page);
        /* Nothing submitted - we have to end page writeback */
        if (!nr_submitted)

diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index a30b203..fef7755 100644 (file)
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -360,10 +360,12 @@ int ext4_mpage_readpages(struct address_space *mapping,
                if (bio == NULL) {
                        struct bio_post_read_ctx *ctx;
 
+                       /*
+                        * bio_alloc will _always_ be able to allocate a bio if
+                        * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
+                        */
                        bio = bio_alloc(GFP_KERNEL,
                                min_t(int, nr_pages, BIO_MAX_PAGES));
-                       if (!bio)
-                               goto set_error_page;
                        ctx = get_bio_post_read_ctx(inode, bio, page->index);
                        if (IS_ERR(ctx)) {
                                bio_put(bio);