gfs2: Fixes to "Implement iomap for block_map"

It turns out that commit 3974320ca6 "Implement iomap for block_map"
introduced a few bugs that trigger occasional failures with xfstest
generic/476:

In gfs2_iomap_begin, we jump to do_alloc when we determine that we are
beyond the end of the allocated metadata (height > ip->i_height).
There, we can end up calling hole_size with a metapath that doesn't
match the current metadata tree, which doesn't make sense.  After
untangling the code at do_alloc, fix this by checking if the block we
are looking for is within the range of allocated metadata.

In addition, add a BUG() in case gfs2_iomap_begin is accidentally called
for reading stuffed files: this is handled separately.  Make sure we
don't truncate iomap->length for reads beyond the end of the file; in
that case, the entire range counts as a hole.

Finally, revert to taking a bitmap write lock when doing allocations.
It's unclear why that change didn't lead to any failures during testing.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index 86863792f36ae1cc60fea8221195824926712e13..86d6a4435c87c31fa27b1ed5b194c2aa626cc801 100644 (file)
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -716,7 +716,7 @@ int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
        __be64 *ptr;
        sector_t lblock;
        sector_t lend;
-       int ret;
+       int ret = 0;
        int eob;
        unsigned int len;
        struct buffer_head *bh;
@@ -728,12 +728,14 @@ int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
                goto out;
        }
 
-       if ((flags & IOMAP_REPORT) && gfs2_is_stuffed(ip)) {
-               gfs2_stuffed_iomap(inode, iomap);
-               if (pos >= iomap->length)
-                       return -ENOENT;
-               ret = 0;
-               goto out;
+       if (gfs2_is_stuffed(ip)) {
+               if (flags & IOMAP_REPORT) {
+                       gfs2_stuffed_iomap(inode, iomap);
+                       if (pos >= iomap->length)
+                               ret = -ENOENT;
+                       goto out;
+               }
+               BUG_ON(!(flags & IOMAP_WRITE));
        }
 
        lblock = pos >> inode->i_blkbits;
@@ -744,7 +746,7 @@ int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
        iomap->type = IOMAP_HOLE;
        iomap->length = (u64)(lend - lblock) << inode->i_blkbits;
        iomap->flags = IOMAP_F_MERGED;
-       bmap_lock(ip, 0);
+       bmap_lock(ip, flags & IOMAP_WRITE);
 
        /*
         * Directory data blocks have a struct gfs2_meta_header header, so the
@@ -787,27 +789,28 @@ int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
                iomap->flags |= IOMAP_F_BOUNDARY;
        iomap->length = (u64)len << inode->i_blkbits;
 
-       ret = 0;
-
 out_release:
        release_metapath(&mp);
-       bmap_unlock(ip, 0);
+       bmap_unlock(ip, flags & IOMAP_WRITE);
 out:
        trace_gfs2_iomap_end(ip, iomap, ret);
        return ret;
 
 do_alloc:
-       if (!(flags & IOMAP_WRITE)) {
-               if (pos >= i_size_read(inode)) {
+       if (flags & IOMAP_WRITE) {
+               ret = gfs2_iomap_alloc(inode, iomap, flags, &mp);
+       } else if (flags & IOMAP_REPORT) {
+               loff_t size = i_size_read(inode);
+               if (pos >= size)
                        ret = -ENOENT;
-                       goto out_release;
-               }
-               ret = 0;
-               iomap->length = hole_size(inode, lblock, &mp);
-               goto out_release;
+               else if (height <= ip->i_height)
+                       iomap->length = hole_size(inode, lblock, &mp);
+               else
+                       iomap->length = size - pos;
+       } else {
+               if (height <= ip->i_height)
+                       iomap->length = hole_size(inode, lblock, &mp);
        }
-
-       ret = gfs2_iomap_alloc(inode, iomap, flags, &mp);
        goto out_release;
 }