erofs: fix bio->bi_max_vecs behavior change

Martin reported an issue that directory read could be hung on the
latest -rc kernel with some certain image. The root cause is that
commit baa2c7c97153 ("block: set .bi_max_vecs as actual allocated
vector number") changes .bi_max_vecs behavior. bio->bi_max_vecs
is set as actual allocated vector number rather than the requested
number now.

Let's avoid using .bi_max_vecs completely instead.

Link: https://lore.kernel.org/r/20210306040438.8084-1-hsiangkao@aol.com
Reported-by: Martin DEVERA <devik@eaxlabs.cz>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
[ Gao Xiang: note that <= 5.11 kernels are not impacted. ]
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index f88851c5c250b5608a4f40fc221ddee9fa8e2108..1249e74b3bf04267cf2f67dfd5af4596e0e9bdcf 100644 (file)
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -129,6 +129,7 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
                                              struct page *page,
                                              erofs_off_t *last_block,
                                              unsigned int nblocks,
+                                             unsigned int *eblks,
                                              bool ra)
 {
        struct inode *const inode = mapping->host;
@@ -145,8 +146,7 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
 
        /* note that for readpage case, bio also equals to NULL */
        if (bio &&
-           /* not continuous */
-           *last_block + 1 != current_block) {
+           (*last_block + 1 != current_block || !*eblks)) {
 submit_bio_retry:
                submit_bio(bio);
                bio = NULL;
@@ -216,7 +216,8 @@ submit_bio_retry:
                if (nblocks > DIV_ROUND_UP(map.m_plen, PAGE_SIZE))
                        nblocks = DIV_ROUND_UP(map.m_plen, PAGE_SIZE);
 
-               bio = bio_alloc(GFP_NOIO, bio_max_segs(nblocks));
+               *eblks = bio_max_segs(nblocks);
+               bio = bio_alloc(GFP_NOIO, *eblks);
 
                bio->bi_end_io = erofs_readendio;
                bio_set_dev(bio, sb->s_bdev);
@@ -229,16 +230,8 @@ submit_bio_retry:
        /* out of the extent or bio is full */
        if (err < PAGE_SIZE)
                goto submit_bio_retry;
-
+       --*eblks;
        *last_block = current_block;
-
-       /* shift in advance in case of it followed by too many gaps */
-       if (bio->bi_iter.bi_size >= bio->bi_max_vecs * PAGE_SIZE) {
-               /* err should reassign to 0 after submitting */
-               err = 0;
-               goto submit_bio_out;
-       }
-
        return bio;
 
 err_out:
@@ -252,7 +245,6 @@ has_updated:
 
        /* if updated manually, continuous pages has a gap */
        if (bio)
-submit_bio_out:
                submit_bio(bio);
        return err ? ERR_PTR(err) : NULL;
 }
@@ -264,23 +256,26 @@ submit_bio_out:
 static int erofs_raw_access_readpage(struct file *file, struct page *page)
 {
        erofs_off_t last_block;
+       unsigned int eblks;
        struct bio *bio;
 
        trace_erofs_readpage(page, true);
 
        bio = erofs_read_raw_page(NULL, page->mapping,
-                                 page, &last_block, 1, false);
+                                 page, &last_block, 1, &eblks, false);
 
        if (IS_ERR(bio))
                return PTR_ERR(bio);
 
-       DBG_BUGON(bio); /* since we have only one bio -- must be NULL */
+       if (bio)
+               submit_bio(bio);
        return 0;
 }
 
 static void erofs_raw_access_readahead(struct readahead_control *rac)
 {
        erofs_off_t last_block;
+       unsigned int eblks;
        struct bio *bio = NULL;
        struct page *page;
 
@@ -291,7 +286,7 @@ static void erofs_raw_access_readahead(struct readahead_control *rac)
                prefetchw(&page->flags);
 
                bio = erofs_read_raw_page(bio, rac->mapping, page, &last_block,
-                               readahead_count(rac), true);
+                               readahead_count(rac), &eblks, true);
 
                /* all the page errors are ignored when readahead */
                if (IS_ERR(bio)) {
@@ -305,7 +300,6 @@ static void erofs_raw_access_readahead(struct readahead_control *rac)
                put_page(page);
        }
 
-       /* the rare case (end in gaps) */
        if (bio)
                submit_bio(bio);
 }