Ocfs2-devel Digest, Vol 135, Issue 28

Commit Message

Zhangguanghui June 11, 2015, 3:05 a.m. UTC

I think the patch has a potential risk. as follows

Callback? ocfs2_write_end_nolock->ocfs2_journal_access_di->__ocfs2_journal_access->buffer_uptodate

So it increases the probability triggering BUG in the  __ocfs2_journal_access().

In addition, test results have been confirmed.

Finally, any feedback about this process (positive or negative) would be  greatly appreciated.


From: [e-mail]<mailto:[e-mail]>
Date: 2015-05-31 03:00
To: [e-mail]<mailto:[e-mail]>
Subject: Ocfs2-devel Digest, Vol 135, Issue 28

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Today's Topics:

   1. [PATCH V2] ocfs2: call ocfs2_journal_access_di() before
      ocfs2_journal_dirty() in ocfs2_write_end_nolock() (yangwenfang)


----------------------------------------------------------------------

Message: 1
Date: Sat, 30 May 2015 18:08:43 +0800
From: yangwenfang <[e-mail]>
Subject: [Ocfs2-devel] [PATCH V2] ocfs2: call
        ocfs2_journal_access_di() before ocfs2_journal_dirty() in
        ocfs2_write_end_nolock()
To: Andrew Morton <[e-mail]>, <[e-mail]>
Cc: [e-mail]
Message-ID: <[e-mail]>
Content-Type: text/plain; charset="ISO-8859-1"

1.After we call ocfs2_journal_access_di() in ocfs2_write_begin(),
jbd2_journal_restart() may also be called, in this function
transaction A's t_updates-- and obtains a new transaction B.
If jbd2_journal_commit_transaction() is happened to commit
transaction A, when t_updates==0, it will continue to complete
commit and unfile buffer.

So when jbd2_journal_dirty_metadata(), the handle is pointed a new
transaction B, and the buffer head's journal head is already freed,
jh->b_transaction == NULL, jh->b_next_transaction == NULL,
it returns EINVAL, So it triggers the BUG_ON(status).

thread 1                                          jbd2
ocfs2_write_begin                     jbd2_journal_commit_transaction
ocfs2_write_begin_nolock
  ocfs2_start_trans
    jbd2__journal_start(t_updates+1,
                       transaction A)
    ocfs2_journal_access_di
    ocfs2_write_cluster_by_desc
      ocfs2_mark_extent_written
        ocfs2_change_extent_flag
          ocfs2_split_extent
            ocfs2_extend_rotate_transaction
              jbd2_journal_restart
              (t_updates-1,transaction B) t_updates==0
                                        __jbd2_journal_refile_buffer
                                        (jh->b_transaction = NULL)
ocfs2_write_end
ocfs2_write_end_nolock
    ocfs2_journal_dirty
        jbd2_journal_dirty_metadata(bug)
   ocfs2_commit_trans

2. In ext4, I found that: jbd2_journal_get_write_access() called by
ext4_write_end.
ext4_write_begin
    ext4_journal_start
        __ext4_journal_start_sb
            ext4_journal_check_start
            jbd2__journal_start

ext4_write_end
    ext4_mark_inode_dirty
        ext4_reserve_inode_write
            ext4_journal_get_write_access
                jbd2_journal_get_write_access
        ext4_mark_iloc_dirty
            ext4_do_update_inode
                ext4_handle_dirty_metadata
                    jbd2_journal_dirty_metadata

3.So I think we should put ocfs2_journal_access_di before
ocfs2_journal_dirty in the ocfs2_write_end.
and it works well after my modification.

Signed-off-by: vicky <[e-mail]>
---
 fs/ocfs2/aops.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--
1.7.12.4




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Patch

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index f906a25..f3d7e52 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -2176,10 +2176,7 @@  try_again:
                if (ret)
                        goto out_commit;
        }
-       /*
-        * We don't want this to fail in ocfs2_write_end(), so do it
-        * here.
-        */
+
        ret = ocfs2_journal_access_di(handle, INODE_CACHE(inode), wc->w_di_bh,
                                      OCFS2_JOURNAL_ACCESS_WRITE);
        if (ret) {
@@ -2336,7 +2333,7 @@  int ocfs2_write_end_nolock(struct address_space *mapping,
                           loff_t pos, unsigned len, unsigned copied,
                           struct page *page, void *fsdata)
 {
-       int i;
+       int i, ret;
        unsigned from, to, start = pos & (PAGE_CACHE_SIZE - 1);
        struct inode *inode = mapping->host;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
@@ -2345,6 +2342,14 @@  int ocfs2_write_end_nolock(struct address_space *mapping,
        handle_t *handle = wc->w_handle;
        struct page *tmppage;

+       ret = ocfs2_journal_access_di(handle, INODE_CACHE(inode), wc->w_di_bh,
+                       OCFS2_JOURNAL_ACCESS_WRITE);
+       if (ret) {
+               copied = ret;
+               mlog_errno(ret);
+               goto out;
+       }
+
        if (OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) {
                ocfs2_write_end_inline(inode, pos, len, &copied, di, wc);
                goto out_write_size;
@@ -2400,6 +2405,7 @@  out_write_size:
        ocfs2_update_inode_fsync_trans(handle, inode, 1);
        ocfs2_journal_dirty(handle, wc->w_di_bh);

+out:
        /* unlock pages before dealloc since it needs acquiring j_trans_barrier
         * lock, or it will cause a deadlock since journal commit threads holds
         * this lock and will ask for the page lock when flushing the data.