Re: [PATCH 22/24] xfs: rework xfs_iflush_cluster() dirty inode iteration

Christoph Hellwig
2020-05-23T11:31:36Z

On Fri, May 22, 2020 at 01:50:27PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Now that we have all the dirty inodes attached to the cluster
> buffer, we don't actually have to do radix tree lookups to find
> them. Sure, the radix tree is efficient, but walking a linked list
> of just the dirty inodes attached to the buffer is much better.
>
> We are also no longer dependent on having a locked inode passed into
> the function to determine where to start the lookup. This means we
> can drop it from the function call and treat all inodes the same.
>
> We also make xfs_iflush_cluster skip inodes marked with
> XFS_IRECLAIM. This we avoid races with inodes that reclaim is
> actively referencing or are being re-initialised by inode lookup. If
> they are actually dirty, they'll get written by a future cluster
> flush....
>
> We also add a shutdown check after obtaining the flush lock so that
> we catch inodes that are dirty in memory and may have inconsistent
> state due to the shutdown in progress. We abort these inodes
> directly and so they remove themselves directly from the buffer list
> and the AIL rather than having to wait for the buffer to be failed
> and callbacks run to be processed correctly.

I suspect we should just kill off xfs_iflush_cluster with this, as it
is best split between xfs_iflush and xfs_inode_item_push. POC patch
below, but as part of that I noticed some really odd error handling,
which I'll bring up separately.

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 6f873eca8c916..8784e70626403 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -1102,12 +1102,12 @@ xfs_reclaim_inode(
/*
* Because we use RCU freeing we need to ensure the inode always appears
* to be reclaimed with an invalid inode number when in the free state.
- * We do this as early as possible under the ILOCK so that
- * xfs_iflush_cluster() and xfs_ifree_cluster() can be guaranteed to
- * detect races with us here. By doing this, we guarantee that once
- * xfs_iflush_cluster() or xfs_ifree_cluster() has locked XFS_ILOCK that
- * it will see either a valid inode that will serialise correctly, or it
- * will see an invalid inode that it can skip.
+ * We do this as early as possible under the ILOCK so that xfs_iflush()
+ * and xfs_ifree_cluster() can be guaranteed to detect races with us
+ * here. By doing this, we guarantee that once xfs_iflush() or
+ * xfs_ifree_cluster() has locked XFS_ILOCK that it will see either a
+ * valid inode that will serialise correctly, or it will see an invalid
+ * inode that it can skip.
*/
spin_lock(&ip->i_flags_lock);
ip->i_flags = XFS_IRECLAIM;
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 5bbdb0c5ed172..8b0197a386a0f 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -3431,19 +3431,70 @@ xfs_rename(

int
xfs_iflush(
- struct xfs_inode *ip,
+ struct xfs_inode_log_item *iip,
struct xfs_buf *bp)
{
- struct xfs_inode_log_item *iip = ip->i_itemp;
- struct xfs_dinode *dip;
+ struct xfs_inode *ip = iip->ili_inode;
struct xfs_mount *mp = ip->i_mount;
- int error;
+ struct xfs_dinode *dip;
+ int error = 0;
+
+ /*
+ * Quick and dirty check to avoid locks if possible.
+ */
+ if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK))
+ return 0;
+ if (xfs_ipincount(ip))
+ return 0;
+
+ /*
+ * The inode is still attached to the buffer, which means it is dirty
+ * but reclaim might try to grab it. Check carefully for that, and grab
+ * the ilock while still holding the i_flags_lock to guarantee reclaim
+ * will not be able to reclaim this inode once we drop the i_flags_lock.
+ */
+ spin_lock(&ip->i_flags_lock);
+ ASSERT(!__xfs_iflags_test(ip, XFS_ISTALE));
+ if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK))
+ goto out_unlock_flags_lock;
+
+ /*
+ * ILOCK will pin the inode against reclaim and prevent concurrent
+ * transactions modifying the inode while we are flushing the inode.
+ */
+ if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED))
+ goto out_unlock_flags_lock;
+ spin_unlock(&ip->i_flags_lock);
+
+ /*
+ * Skip inodes that are already flush locked as they have already been
+ * written to the buffer.
+ */
+ if (!xfs_iflock_nowait(ip))
+ goto out_unlock_ilock;
+
+ /*
+ * If we are shut down, unpin and abort the inode now as there is no
+ * point in flushing it to the buffer just to get an IO completion to
+ * abort the buffer and remove it from the AIL.
+ */
+ if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
+ xfs_iunpin_wait(ip);
+ /* xfs_iflush_abort() drops the flush lock */
+ xfs_iflush_abort(ip);
+ error = -EIO;
+ goto out_unlock_ilock;
+ }
+
+ /* don't block waiting on a log force to unpin dirty inodes */
+ if (xfs_ipincount(ip) || xfs_inode_clean(ip)) {
+ xfs_ifunlock(ip);
+ goto out_unlock_ilock;
+ }

- ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL|XFS_ILOCK_SHARED));
- ASSERT(xfs_isiflocked(ip));
ASSERT(ip->i_df.if_format != XFS_DINODE_FMT_BTREE ||
ip->i_df.if_nextents > XFS_IFORK_MAXEXT(ip, XFS_DATA_FORK));
- ASSERT(iip != NULL && iip->ili_fields != 0);
+ ASSERT(iip->ili_fields != 0);
ASSERT(iip->ili_item.li_buf == bp);

dip = xfs_buf_offset(bp, ip->i_imap.im_boffset);
@@ -3574,122 +3625,13 @@ xfs_iflush(

/* generate the checksum. */
xfs_dinode_calc_crc(mp, dip);
- return error;
-}
-
-/*
- * Non-blocking flush of dirty inode metadata into the backing buffer.
- *
- * The caller must have a reference to the inode and hold the cluster buffer
- * locked. The function will walk across all the inodes on the cluster buffer it
- * can find and lock without blocking, and flush them to the cluster buffer.
- *
- * On success, the caller must write out the buffer returned in *bp and
- * release it. On failure, the filesystem will be shut down, the buffer will
- * have been unlocked and released, and EFSCORRUPTED will be returned.
- */
-int
-xfs_iflush_cluster(
- struct xfs_buf *bp)
-{
- struct xfs_mount *mp = bp->b_mount;
- struct xfs_log_item *lip, *n;
- struct xfs_inode *ip;
- struct xfs_inode_log_item *iip;
- int clcount = 0;
- int error = 0;

- /*
- * We must use the safe variant here as on shutdown xfs_iflush_abort()
- * can remove itself from the list.
- */
- list_for_each_entry_safe(lip, n, &bp->b_li_list, li_bio_list) {
- iip = (struct xfs_inode_log_item *)lip;
- ip = iip->ili_inode;
-
- /*
- * Quick and dirty check to avoid locks if possible.
- */
- if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK))
- continue;
- if (xfs_ipincount(ip))
- continue;
-
- /*
- * The inode is still attached to the buffer, which means it is
- * dirty but reclaim might try to grab it. Check carefully for
- * that, and grab the ilock while still holding the i_flags_lock
- * to guarantee reclaim will not be able to reclaim this inode
- * once we drop the i_flags_lock.
- */
- spin_lock(&ip->i_flags_lock);
- ASSERT(!__xfs_iflags_test(ip, XFS_ISTALE));
- if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK)) {
- spin_unlock(&ip->i_flags_lock);
- continue;
- }
-
- /*
- * ILOCK will pin the inode against reclaim and prevent
- * concurrent transactions modifying the inode while we are
- * flushing the inode.
- */
- if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED)) {
- spin_unlock(&ip->i_flags_lock);
- continue;
- }
- spin_unlock(&ip->i_flags_lock);
-
- /*
- * Skip inodes that are already flush locked as they have
- * already been written to the buffer.
- */
- if (!xfs_iflock_nowait(ip)) {
- xfs_iunlock(ip, XFS_ILOCK_SHARED);
- continue;
- }
-
- /*
- * If we are shut down, unpin and abort the inode now as there
- * is no point in flushing it to the buffer just to get an IO
- * completion to abort the buffer and remove it from the AIL.
- */
- if (XFS_FORCED_SHUTDOWN(mp)) {
- xfs_iunpin_wait(ip);
- /* xfs_iflush_abort() drops the flush lock */
- xfs_iflush_abort(ip);
- xfs_iunlock(ip, XFS_ILOCK_SHARED);
- error = EIO;
- continue;
- }
-
- /* don't block waiting on a log force to unpin dirty inodes */
- if (xfs_ipincount(ip)) {
- xfs_ifunlock(ip);
- xfs_iunlock(ip, XFS_ILOCK_SHARED);
- continue;
- }
-
- if (!xfs_inode_clean(ip))
- error = xfs_iflush(ip, bp);
- else
- xfs_ifunlock(ip);
- xfs_iunlock(ip, XFS_ILOCK_SHARED);
- if (error)
- break;
- clcount++;
- }
-
- if (clcount) {
- XFS_STATS_INC(mp, xs_icluster_flushcnt);
- XFS_STATS_ADD(mp, xs_icluster_flushinode, clcount);
- }
+out_unlock_ilock:
+ xfs_iunlock(ip, XFS_ILOCK_SHARED);
+ return error;

- if (error) {
- bp->b_flags |= XBF_ASYNC;
- xfs_buf_ioend_fail(bp);
- xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
- }
+out_unlock_flags_lock:
+ spin_unlock(&ip->i_flags_lock);
return error;
}

diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index b93cf9076df8a..870e6768e119e 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -427,7 +427,7 @@ int xfs_log_force_inode(struct xfs_inode *ip);
void xfs_iunpin_wait(xfs_inode_t *);
#define xfs_ipincount(ip) ((unsigned int) atomic_read(&ip->i_pincount))

-int xfs_iflush_cluster(struct xfs_buf *);
+int xfs_iflush(struct xfs_inode_log_item *iip, struct xfs_buf *bp);
void xfs_lock_two_inodes(struct xfs_inode *ip0, uint ip0_mode,
struct xfs_inode *ip1, uint ip1_mode);

diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
index 4dd4f45dcc46e..b82d7f3628745 100644
--- a/fs/xfs/xfs_inode_item.c
+++ b/fs/xfs/xfs_inode_item.c
@@ -501,8 +501,10 @@ xfs_inode_item_push(
struct xfs_inode_log_item *iip = INODE_ITEM(lip);
struct xfs_inode *ip = iip->ili_inode;
struct xfs_buf *bp = lip->li_buf;
+ struct xfs_mount *mp = bp->b_mount;
+ struct xfs_log_item *l, *n;
uint rval = XFS_ITEM_SUCCESS;
- int error;
+ int clcount = 0;

ASSERT(iip->ili_item.li_buf);

@@ -530,17 +532,34 @@ xfs_inode_item_push(
* for IO until we queue it for delwri submission.
*/
xfs_buf_hold(bp);
- error = xfs_iflush_cluster(bp);
- if (!error) {
- if (!xfs_buf_delwri_queue(bp, buffer_list)) {
- ASSERT(0);
- rval = XFS_ITEM_FLUSHING;
+
+ /*
+ * We must use the safe variant here as on shutdown xfs_iflush_abort()
+ * can remove itself from the list.
+ */
+ list_for_each_entry_safe(l, n, &bp->b_li_list, li_bio_list) {
+ if (xfs_iflush(INODE_ITEM(l), bp)) {
+ bp->b_flags |= XBF_ASYNC;
+ xfs_buf_ioend_fail(bp);
+ xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
+ rval = XFS_ITEM_LOCKED;
+ goto out_unlock;
}
- xfs_buf_relse(bp);
- } else {
- rval = XFS_ITEM_LOCKED;
+ clcount++;
+ }
+
+ if (clcount) {
+ XFS_STATS_INC(mp, xs_icluster_flushcnt);
+ XFS_STATS_ADD(mp, xs_icluster_flushinode, clcount);
+ }
+
+ if (!xfs_buf_delwri_queue(bp, buffer_list)) {
+ ASSERT(0);
+ rval = XFS_ITEM_FLUSHING;
}
+ xfs_buf_relse(bp);

+out_unlock:
spin_lock(&lip->li_ailp->ail_lock);
return rval;
}