On Thu, Jun 04, 2020 at 05:46:04PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> 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.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
> fs/xfs/xfs_inode.c | 148 ++++++++++++++++------------------------
> fs/xfs/xfs_inode.h | 2 +-
> fs/xfs/xfs_inode_item.c | 2 +-
> 3 files changed, 62 insertions(+), 90 deletions(-)
>
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 8566bd0f4334d..931a483d5b316 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -3611,117 +3611,94 @@ xfs_iflush(
> */
> int
> xfs_iflush_cluster(
> - struct xfs_inode *ip,
> struct xfs_buf *bp)
> {
...
> + /*
> + * 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;
>
> /*
> - * because this is an RCU protected lookup, we could find a
> - * recently freed or even reallocated inode during the lookup.
> - * We need to check under the i_flags_lock for a valid inode
> - * here. Skip it if it is not valid or the wrong inode.
> + * Quick and dirty check to avoid locks if possible.
> */
> - spin_lock(&cip->i_flags_lock);
> - if (!cip->i_ino ||
> - __xfs_iflags_test(cip, XFS_ISTALE)) {
> - spin_unlock(&cip->i_flags_lock);
> + if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK))
> + continue;
> + if (xfs_ipincount(ip))
> continue;
> - }
>
> /*
> - * Once we fall off the end of the cluster, no point checking
> - * any more inodes in the list because they will also all be
> - * outside the cluster.
> + * 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.
> */
> - if ((XFS_INO_TO_AGINO(mp, cip->i_ino) & mask) != first_index) {
> - spin_unlock(&cip->i_flags_lock);
> - break;
> + spin_lock(&ip->i_flags_lock);
> + ASSERT(!__xfs_iflags_test(ip, XFS_ISTALE));
What prevents a race with staling an inode here? The push open codes an
unlocked (i.e. no memory barrier) check before it acquires the buffer
lock, so afaict it's technically possible to race and grab the buffer
immediately after the cluster was freed. If that could happen, it looks
like we'd also queue the buffer for write.
That also raises the question.. between this patch and the earlier push
rework, why do we queue the buffer for write when nothing might have
been flushed by this call?
> + if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK)) {
> + spin_unlock(&ip->i_flags_lock);
> + continue;
> }
> - spin_unlock(&cip->i_flags_lock);
>
> /*
> - * Do an un-protected check to see if the inode is dirty and
> - * is a candidate for flushing. These checks will be repeated
> - * later after the appropriate locks are acquired.
> + * ILOCK will pin the inode against reclaim and prevent
> + * concurrent transactions modifying the inode while we are
> + * flushing the inode.
> */
> - if (xfs_inode_clean(cip) && xfs_ipincount(cip) == 0)
> + if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED)) {
> + spin_unlock(&ip->i_flags_lock);
> continue;
> + }
> + spin_unlock(&ip->i_flags_lock);
>
> /*
> - * Try to get locks. If any are unavailable or it is pinned,
> - * then this inode cannot be flushed and is skipped.
> + * Skip inodes that are already flush locked as they have
> + * already been written to the buffer.
> */
> -
> - if (!xfs_ilock_nowait(cip, XFS_ILOCK_SHARED))
> - continue;
> - if (!xfs_iflock_nowait(cip)) {
> - xfs_iunlock(cip, XFS_ILOCK_SHARED);
> - continue;
> - }
> - if (xfs_ipincount(cip)) {
> - xfs_ifunlock(cip);
> - xfs_iunlock(cip, XFS_ILOCK_SHARED);
> + if (!xfs_iflock_nowait(ip)) {
> + xfs_iunlock(ip, XFS_ILOCK_SHARED);
> continue;
> }
>
> -
> /*
> - * Check the inode number again, just to be certain we are not
> - * racing with freeing in xfs_reclaim_inode(). See the comments
> - * in that function for more information as to why the initial
> - * check is not sufficient.
> + * 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 (!cip->i_ino) {
> - xfs_ifunlock(cip);
> - xfs_iunlock(cip, XFS_ILOCK_SHARED);
> + if (XFS_FORCED_SHUTDOWN(mp)) {
> + xfs_iunpin_wait(ip);
Note that we have an unlocked check above that skips pinned inodes.
Brian
> + /* xfs_iflush_abort() drops the flush lock */
> + xfs_iflush_abort(ip);
> + xfs_iunlock(ip, XFS_ILOCK_SHARED);
> + error = -EIO;
> continue;
> }
>
> - /*
> - * arriving here means that this inode can be flushed. First
> - * re-check that it's dirty before flushing.
> - */
> - if (!xfs_inode_clean(cip)) {
> - error = xfs_iflush(cip, bp);
> - if (error) {
> - xfs_iunlock(cip, XFS_ILOCK_SHARED);
> - goto out_free;
> - }
> - clcount++;
> - } else {
> - xfs_ifunlock(cip);
> + /* 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;
> }
> - xfs_iunlock(cip, XFS_ILOCK_SHARED);
> +
> + 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) {
> @@ -3729,11 +3706,6 @@ xfs_iflush_cluster(
> XFS_STATS_ADD(mp, xs_icluster_flushinode, clcount);
> }
>
> -out_free:
> - rcu_read_unlock();
> - kmem_free(cilist);
> -out_put:
> - xfs_perag_put(pag);
> if (error) {
> bp->b_flags |= XBF_ASYNC;
> xfs_buf_ioend_fail(bp);
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index d1109eb13ba2e..b93cf9076df8a 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_inode *, struct xfs_buf *);
> +int xfs_iflush_cluster(struct xfs_buf *);
> 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 326547e89cb6b..dee7385466f83 100644
> --- a/fs/xfs/xfs_inode_item.c
> +++ b/fs/xfs/xfs_inode_item.c
> @@ -511,7 +511,7 @@ xfs_inode_item_push(
> * reference for IO until we queue the buffer for delwri submission.
> */
> xfs_buf_hold(bp);
> - error = xfs_iflush_cluster(ip, bp);
> + error = xfs_iflush_cluster(bp);
> if (!error) {
> if (!xfs_buf_delwri_queue(bp, buffer_list))
> rval = XFS_ITEM_FLUSHING;
> --
> 2.26.2.761.g0e0b3e54be
>
