jbd2: Add barrier not supported test to journal_wait_on_commit_record

Xen doesn't report that barriers are not supported until buffer I/O is
reported as completed, instead of when the buffer I/O is submitted.
Add a check and a fallback codepath to journal_wait_on_commit_record()
to detect this case, so that attempts to mount ext4 filesystems on
LVM/devicemapper devices on Xen guests don't blow up with an "Aborting
journal on device XXX"; "Remounting filesystem read-only" error.

Thanks to Andreas Sundstrom for reporting this issue.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

1 files changed, 25 insertions, 2 deletions

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index ebc667bc54a8..6393fd0d804e 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -25,6 +25,7 @@
 #include <linux/crc32.h>
 #include <linux/writeback.h>
 #include <linux/backing-dev.h>
+#include <linux/bio.h>
 
 /*
  * Default IO end handler for temporary BJ_IO buffer_heads.
@@ -168,12 +169,34 @@ static int journal_submit_commit_record(journal_t *journal,
  * This function along with journal_submit_commit_record
  * allows to write the commit record asynchronously.
  */
-static int journal_wait_on_commit_record(struct buffer_head *bh)
+static int journal_wait_on_commit_record(journal_t *journal,
+                                         struct buffer_head *bh)
 {
         int ret = 0;
 
+retry:
         clear_buffer_dirty(bh);
         wait_on_buffer(bh);
+        if (buffer_eopnotsupp(bh) && (journal->j_flags & JBD2_BARRIER)) {
+                printk(KERN_WARNING
+                       "JBD2: wait_on_commit_record: sync failed on %s - "
+                       "disabling barriers\n", journal->j_devname);
+                spin_lock(&journal->j_state_lock);
+                journal->j_flags &= ~JBD2_BARRIER;
+                spin_unlock(&journal->j_state_lock);
+
+                lock_buffer(bh);
+                clear_buffer_dirty(bh);
+                set_buffer_uptodate(bh);
+                bh->b_end_io = journal_end_buffer_io_sync;
+
+                ret = submit_bh(WRITE_SYNC, bh);
+                if (ret) {
+                        unlock_buffer(bh);
+                        return ret;
+                }
+                goto retry;
+        }
 
         if (unlikely(!buffer_uptodate(bh)))
                 ret = -EIO;
@@ -799,7 +822,7 @@ wait_for_iobuf:
                         __jbd2_journal_abort_hard(journal);
         }
         if (!err && !is_journal_aborted(journal))
-                err = journal_wait_on_commit_record(cbh);
+                err = journal_wait_on_commit_record(journal, cbh);
 
         if (err)
                 jbd2_journal_abort(journal, err);