linux-ext4 - ext3/jbd: Avoid WARN() messages when failing to write the superblock

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Message-ID: <20101004193505.GC25624@tux1.beaverton.ibm.com>
Date:	Mon, 4 Oct 2010 12:35:05 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>
Cc:	linux-ext4@...r.kernel.org
Subject: ext3/jbd: Avoid WARN() messages when failing to write the
	superblock

This fixes a WARN backtrace in mark_buffer_dirty() that occurs during unmount
when the underlying block device is removed.  This bug has been seen on System
Z when removing all paths from a multipath-backed ext3 mount; on System P when
injecting enough PCI EEH errors to make the SCSI controller go offline; and
similar warnings have been seen (and patched) with ext2/ext4.

The super block update from a previous operation has marked the buffer as in
error, and the flag has to be cleared before doing the update.  (Similar code
already exists in ext4).

Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
---

 fs/ext3/super.c  |   24 +++++++++++++++++++++++-
 fs/jbd/journal.c |   30 ++++++++++++++++++++++++++++--
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 5dbf4db..5a19796 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -2361,6 +2361,21 @@ static int ext3_commit_super(struct super_block *sb,
 
 	if (!sbh)
 		return error;
+
+	if (buffer_write_io_error(sbh)) {
+		/*
+		 * Oh, dear.  A previous attempt to write the
+		 * superblock failed.  This could happen because the
+		 * USB device was yanked out.  Or it could happen to
+		 * be a transient write error and maybe the block will
+		 * be remapped.  Nothing we can do but to retry the
+		 * write and hope for the best.
+		 */
+		printk(KERN_ERR "ext3: previous I/O error to "
+		       "superblock detected for %s.\n", sb->s_id);
+		clear_buffer_write_io_error(sbh);
+		set_buffer_uptodate(sbh);
+	}
 	/*
 	 * If the file system is mounted read-only, don't update the
 	 * superblock write time.  This avoids updating the superblock
@@ -2377,8 +2392,15 @@ static int ext3_commit_super(struct super_block *sb,
 	es->s_free_inodes_count = cpu_to_le32(ext3_count_free_inodes(sb));
 	BUFFER_TRACE(sbh, "marking dirty");
 	mark_buffer_dirty(sbh);
-	if (sync)
+	if (sync) {
 		error = sync_dirty_buffer(sbh);
+		if (buffer_write_io_error(sbh)) {
+			printk(KERN_ERR "ext3: I/O error while writing "
+			       "superblock for %s.\n", sb->s_id);
+			clear_buffer_write_io_error(sbh);
+			set_buffer_uptodate(sbh);
+		}
+	}
 	return error;
 }
 
diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index 2c4b1f1..8bfd226 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -84,6 +84,7 @@ EXPORT_SYMBOL(journal_force_commit);
 
 static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
 static void __journal_abort_soft (journal_t *journal, int errno);
+static const char *journal_dev_name(journal_t *journal, char *buffer);
 
 /*
  * Helper function used to manage commit timeouts
@@ -1010,6 +1011,23 @@ void journal_update_superblock(journal_t *journal, int wait)
 		goto out;
 	}
 
+	if (buffer_write_io_error(bh)) {
+		char b[BDEVNAME_SIZE];
+		/*
+		 * Oh, dear.  A previous attempt to write the journal
+		 * superblock failed.  This could happen because the
+		 * USB device was yanked out.  Or it could happen to
+		 * be a transient write error and maybe the block will
+		 * be remapped.  Nothing we can do but to retry the
+		 * write and hope for the best.
+		 */
+		printk(KERN_ERR "JBD: previous I/O error detected "
+		       "for journal superblock update for %s.\n",
+		       journal_dev_name(journal, b));
+		clear_buffer_write_io_error(bh);
+		set_buffer_uptodate(bh);
+	}
+
 	spin_lock(&journal->j_state_lock);
 	jbd_debug(1,"JBD: updating superblock (start %u, seq %d, errno %d)\n",
 		  journal->j_tail, journal->j_tail_sequence, journal->j_errno);
@@ -1021,9 +1039,17 @@ void journal_update_superblock(journal_t *journal, int wait)
 
 	BUFFER_TRACE(bh, "marking dirty");
 	mark_buffer_dirty(bh);
-	if (wait)
+	if (wait) {
 		sync_dirty_buffer(bh);
-	else
+		if (buffer_write_io_error(bh)) {
+			char b[BDEVNAME_SIZE];
+			printk(KERN_ERR "JBD: I/O error detected "
+			       "when updating journal superblock for %s.\n",
+			       journal_dev_name(journal, b));
+			clear_buffer_write_io_error(bh);
+			set_buffer_uptodate(bh);
+		}
+	} else
 		write_dirty_buffer(bh, WRITE);
 
 out:
--
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