ext4, jbd2: add an optimized bmap for the journal inode

The generic bmap() function exported by the VFS takes locks and does
checks that are not necessary for the journal inode.  So allow the
file system to set a journal-optimized bmap function in
journal->j_bmap.

Reported-by: syzbot+9543479984ae9e576000@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=e4aaa78795e490421c79f76ec3679006c8ff4cf0
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2192b4111442727903c92104ba180e29547f2362..46b7345d2b6a91d68fb598571a4be4e43901f779 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5742,6 +5742,28 @@ static struct inode *ext4_get_journal_inode(struct super_block *sb,
        return journal_inode;
 }
 
+static int ext4_journal_bmap(journal_t *journal, sector_t *block)
+{
+       struct ext4_map_blocks map;
+       int ret;
+
+       if (journal->j_inode == NULL)
+               return 0;
+
+       map.m_lblk = *block;
+       map.m_len = 1;
+       ret = ext4_map_blocks(NULL, journal->j_inode, &map, 0);
+       if (ret <= 0) {
+               ext4_msg(journal->j_inode->i_sb, KERN_CRIT,
+                        "journal bmap failed: block %llu ret %d\n",
+                        *block, ret);
+               jbd2_journal_abort(journal, ret ? ret : -EIO);
+               return ret;
+       }
+       *block = map.m_pblk;
+       return 0;
+}
+
 static journal_t *ext4_get_journal(struct super_block *sb,
                                   unsigned int journal_inum)
 {
@@ -5762,6 +5784,7 @@ static journal_t *ext4_get_journal(struct super_block *sb,
                return NULL;
        }
        journal->j_private = sb;
+       journal->j_bmap = ext4_journal_bmap;
        ext4_init_journal_params(sb, journal);
        return journal;
 }

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 2696f43e7239f809bcc1ff7b784ea51d94fa6f99..c84f588fdcd038e8b7dd85f5384710c12cd31025 100644 (file)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -970,10 +970,13 @@ int jbd2_journal_bmap(journal_t *journal, unsigned long blocknr,
 {
        int err = 0;
        unsigned long long ret;
-       sector_t block = 0;
+       sector_t block = blocknr;
 
-       if (journal->j_inode) {
-               block = blocknr;
+       if (journal->j_bmap) {
+               err = journal->j_bmap(journal, &block);
+               if (err == 0)
+                       *retp = block;
+       } else if (journal->j_inode) {
                ret = bmap(journal->j_inode, &block);
 
                if (ret || !block) {

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 2170e0cc279d5cb823f5be2cca53cc3d9b5eece8..6ffa34c51a11be21bea2dc0832562cb1ac54e72c 100644 (file)
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1308,6 +1308,14 @@ struct journal_s
                                    struct buffer_head *bh,
                                    enum passtype pass, int off,
                                    tid_t expected_commit_id);
+
+       /**
+        * @j_bmap:
+        *
+        * Bmap function that should be used instead of the generic
+        * VFS bmap function.
+        */
+       int (*j_bmap)(struct journal_s *journal, sector_t *block);
 };
 
 #define jbd2_might_wait_for_commit(j) \