Re: [PATCH] xfs: Introduce permanent async buffer write IO failures

Eric Sandeen
2015-02-19T22:39:13Z

What about something along these lines (rough, but works) -
shut down the fs after enough time goes by with sequential errors
and no success, on the same buffer (based on your patch...)

One thing that still happens is a lot of error spew during the
retries, maybe we can make more use of XBF_WRITE_FAIL to only
print errors once?

Based-on-patch-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>

diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 75ff5d5..13c47a1 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -181,6 +181,7 @@ typedef struct xfs_buf {
unsigned int b_page_count; /* size of page array */
unsigned int b_offset; /* page offset in first page */
int b_error; /* error code on I/O */
+ unsigned long b_first_error_time;
const struct xfs_buf_ops *b_ops;

#ifdef XFS_BUF_LOCK_TRACKING
diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 507d96a..4751c5f 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -1041,14 +1041,13 @@ xfs_buf_do_callbacks(
}

/*
- * This is the iodone() function for buffers which have had callbacks
- * attached to them by xfs_buf_attach_iodone(). It should remove each
- * log item from the buffer's list and call the callback of each in turn.
- * When done, the buffer's fsprivate field is set to NULL and the buffer
- * is unlocked with a call to iodone().
+ * Process a write IO error on a buffer with active log items.
+ *
+ * Returns true if the buffer has been completed and released, false if callback
+ * processing still needs to be performed and the IO completed.
*/
-void
-xfs_buf_iodone_callbacks(
+static bool
+xfs_buf_iodone_callback_error(
struct xfs_buf *bp)
{
struct xfs_log_item *lip = bp->b_fspriv;
@@ -1056,19 +1055,12 @@ xfs_buf_iodone_callbacks(
static ulong lasttime;
static xfs_buftarg_t *lasttarg;

- if (likely(!bp->b_error))
- goto do_callbacks;
-
/*
* If we've already decided to shutdown the filesystem because of
* I/O errors, there's no point in giving this a retry.
*/
- if (XFS_FORCED_SHUTDOWN(mp)) {
- xfs_buf_stale(bp);
- XFS_BUF_DONE(bp);
- trace_xfs_buf_item_iodone(bp, _RET_IP_);
- goto do_callbacks;
- }
+ if (XFS_FORCED_SHUTDOWN(mp))
+ goto out_stale;

if (bp->b_target != lasttarg ||
time_after(jiffies, (lasttime + 5*HZ))) {
@@ -1077,45 +1069,70 @@ xfs_buf_iodone_callbacks(
}
lasttarg = bp->b_target;

+ /* synchronous writes will have callers process the error */
+ if (!(bp->b_flags & XBF_ASYNC))
+ goto out_stale;
+
+ trace_xfs_buf_item_iodone_async(bp, _RET_IP_);
+ ASSERT(bp->b_iodone != NULL);
+
/*
* If the write was asynchronous then no one will be looking for the
- * error. Clear the error state and write the buffer out again.
- *
- * XXX: This helps against transient write errors, but we need to find
- * a way to shut the filesystem down if the writes keep failing.
- *
- * In practice we'll shut the filesystem down soon as non-transient
- * errors tend to affect the whole device and a failing log write
- * will make us give up. But we really ought to do better here.
+ * error. If this is the first failure, clear the error state and write
+ * the buffer out again.
*/
- if (XFS_BUF_ISASYNC(bp)) {
- ASSERT(bp->b_iodone != NULL);
-
- trace_xfs_buf_item_iodone_async(bp, _RET_IP_);
-
- xfs_buf_ioerror(bp, 0); /* errno of 0 unsets the flag */
-
- if (!(bp->b_flags & (XBF_STALE|XBF_WRITE_FAIL))) {
- bp->b_flags |= XBF_WRITE | XBF_ASYNC |
- XBF_DONE | XBF_WRITE_FAIL;
- xfs_buf_submit(bp);
- } else {
- xfs_buf_relse(bp);
- }
-
- return;
+ if (!(bp->b_flags & (XBF_STALE|XBF_WRITE_FAIL))) {
+ if (!bp->b_first_error_time)
+ bp->b_first_error_time = get_seconds();
+ xfs_buf_ioerror(bp, 0);
+ bp->b_flags |= XBF_WRITE | XBF_ASYNC |
+ XBF_DONE | XBF_WRITE_FAIL;
+ xfs_buf_submit(bp);
+ return true;
}

/*
- * If the write of the buffer was synchronous, we want to make
- * sure to return the error to the caller of xfs_bwrite().
+ * Repeated failure on an async write.
+ *
+ * Let things retry for <tuneable handwave> 60s, then give up.
+ * XXX handle seconds wrap?
*/
+ if (get_seconds() - bp->b_first_error_time > 60) {
+ xfs_err(mp, "too many errors, giving up");
+ xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
+ goto out_stale;
+ }
+
+ xfs_buf_relse(bp);
+ return true;
+
+out_stale:
xfs_buf_stale(bp);
XFS_BUF_DONE(bp);
-
trace_xfs_buf_error_relse(bp, _RET_IP_);
+ return false;
+}
+
+/*
+ * This is the iodone() function for buffers which have had callbacks attached
+ * to them by xfs_buf_attach_iodone(). We need to iterate the items on the
+ * callback list, mark the buffer as having no more callbacks and then push the
+ * buffer through IO completion processing.
+ */
+void
+xfs_buf_iodone_callbacks(
+ struct xfs_buf *bp)
+{
+ /*
+ * If there is an error, process it. Some errors require us
+ * to run callbacks after failure processing is done so we
+ * detect that and take appropriate action.
+ */
+ if (bp->b_error && xfs_buf_iodone_callback_error(bp))
+ return;

-do_callbacks:
+ /* zero out error timer if we're good */
+ bp->b_first_error_time = 0;
xfs_buf_do_callbacks(bp);
bp->b_fspriv = NULL;
bp->b_iodone = NULL;