Re: [PATCH 01/13] xfs: xfs_iflock is no longer a completion

Darrick J. Wong
2020-08-18T23:45:06Z

On Wed, Aug 12, 2020 at 07:25:44PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> With the recent rework of the inode cluster flushing, we no longer
> ever wait on the the inode flush "lock". It was never a lock in the
> first place, just a completion to allow callers to wait for inode IO
> to complete. We now never wait for flush completion as all inode
> flushing is non-blocking. Hence we can get rid of all the iflock
> infrastructure and instead just set and check a state flag.
>
> Rename the XFS_IFLOCK flag to XFS_IFLUSHING, convert all the
> xfs_iflock_nowait() test-and-set operations on that flag, and
> replace all the xfs_ifunlock() calls to clear operations.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Hm. I /think/ this looks fairly straightforward, at least once I
realized that nobody calls xfs_iflock anymore.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
> fs/xfs/xfs_icache.c | 17 ++++------
> fs/xfs/xfs_inode.c | 73 +++++++++++++++--------------------------
> fs/xfs/xfs_inode.h | 33 +------------------
> fs/xfs/xfs_inode_item.c | 15 ++++-----
> fs/xfs/xfs_inode_item.h | 4 +--
> fs/xfs/xfs_mount.c | 11 ++++---
> fs/xfs/xfs_super.c | 10 +++---
> 7 files changed, 55 insertions(+), 108 deletions(-)
>
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index 101028ebb571..aa6aad258670 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -52,7 +52,6 @@ xfs_inode_alloc(
>
> XFS_STATS_INC(mp, vn_active);
> ASSERT(atomic_read(&ip->i_pincount) == 0);
> - ASSERT(!xfs_isiflocked(ip));
> ASSERT(ip->i_ino == 0);
>
> /* initialise the xfs inode */
> @@ -123,7 +122,7 @@ void
> xfs_inode_free(
> struct xfs_inode *ip)
> {
> - ASSERT(!xfs_isiflocked(ip));
> + ASSERT(!xfs_iflags_test(ip, XFS_IFLUSHING));
>
> /*
> * Because we use RCU freeing we need to ensure the inode always
> @@ -1035,23 +1034,21 @@ xfs_reclaim_inode(
>
> if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
> goto out;
> - if (!xfs_iflock_nowait(ip))
> + if (xfs_iflags_test_and_set(ip, XFS_IFLUSHING))
> goto out_iunlock;
>
> if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
> xfs_iunpin_wait(ip);
> - /* xfs_iflush_abort() drops the flush lock */
> xfs_iflush_abort(ip);
> goto reclaim;
> }
> if (xfs_ipincount(ip))
> - goto out_ifunlock;
> + goto out_clear_flush;
> if (!xfs_inode_clean(ip))
> - goto out_ifunlock;
> + goto out_clear_flush;
>
> - xfs_ifunlock(ip);
> + xfs_iflags_clear(ip, XFS_IFLUSHING);
> reclaim:
> - ASSERT(!xfs_isiflocked(ip));
>
> /*
> * Because we use RCU freeing we need to ensure the inode always appears
> @@ -1101,8 +1098,8 @@ xfs_reclaim_inode(
> __xfs_inode_free(ip);
> return;
>
> -out_ifunlock:
> - xfs_ifunlock(ip);
> +out_clear_flush:
> + xfs_iflags_clear(ip, XFS_IFLUSHING);
> out_iunlock:
> xfs_iunlock(ip, XFS_ILOCK_EXCL);
> out:
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index c06129cffba9..2072bd25989a 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -598,22 +598,6 @@ xfs_lock_two_inodes(
> }
> }
>
> -void
> -__xfs_iflock(
> - struct xfs_inode *ip)
> -{
> - wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_IFLOCK_BIT);
> - DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_IFLOCK_BIT);
> -
> - do {
> - prepare_to_wait_exclusive(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
> - if (xfs_isiflocked(ip))
> - io_schedule();
> - } while (!xfs_iflock_nowait(ip));
> -
> - finish_wait(wq, &wait.wq_entry);
> -}
> -
> STATIC uint
> _xfs_dic2xflags(
> uint16_t di_flags,
> @@ -2531,11 +2515,8 @@ xfs_ifree_mark_inode_stale(
> * valid, the wrong inode or stale.
> */
> spin_lock(&ip->i_flags_lock);
> - if (ip->i_ino != inum || __xfs_iflags_test(ip, XFS_ISTALE)) {
> - spin_unlock(&ip->i_flags_lock);
> - rcu_read_unlock();
> - return;
> - }
> + if (ip->i_ino != inum || __xfs_iflags_test(ip, XFS_ISTALE))
> + goto out_iflags_unlock;
>
> /*
> * Don't try to lock/unlock the current inode, but we _cannot_ skip the
> @@ -2552,16 +2533,14 @@ xfs_ifree_mark_inode_stale(
> }
> }
> ip->i_flags |= XFS_ISTALE;
> - spin_unlock(&ip->i_flags_lock);
> - rcu_read_unlock();
>
> /*
> - * If we can't get the flush lock, the inode is already attached. All
> + * If the inode is flushing, it is already attached to the buffer. All
> * we needed to do here is mark the inode stale so buffer IO completion
> * will remove it from the AIL.
> */
> iip = ip->i_itemp;
> - if (!xfs_iflock_nowait(ip)) {
> + if (__xfs_iflags_test(ip, XFS_IFLUSHING)) {
> ASSERT(!list_empty(&iip->ili_item.li_bio_list));
> ASSERT(iip->ili_last_fields);
> goto out_iunlock;
> @@ -2573,10 +2552,12 @@ xfs_ifree_mark_inode_stale(
> * commit as the flock synchronises removal of the inode from the
> * cluster buffer against inode reclaim.
> */
> - if (!iip || list_empty(&iip->ili_item.li_bio_list)) {
> - xfs_ifunlock(ip);
> + if (!iip || list_empty(&iip->ili_item.li_bio_list))
> goto out_iunlock;
> - }
> +
> + __xfs_iflags_set(ip, XFS_IFLUSHING);
> + spin_unlock(&ip->i_flags_lock);
> + rcu_read_unlock();
>
> /* we have a dirty inode in memory that has not yet been flushed. */
> spin_lock(&iip->ili_lock);
> @@ -2586,9 +2567,16 @@ xfs_ifree_mark_inode_stale(
> spin_unlock(&iip->ili_lock);
> ASSERT(iip->ili_last_fields);
>
> + if (ip != free_ip)
> + xfs_iunlock(ip, XFS_ILOCK_EXCL);
> + return;
> +
> out_iunlock:
> if (ip != free_ip)
> xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +out_iflags_unlock:
> + spin_unlock(&ip->i_flags_lock);
> + rcu_read_unlock();
> }
>
> /*
> @@ -2631,8 +2619,9 @@ xfs_ifree_cluster(
>
> /*
> * We obtain and lock the backing buffer first in the process
> - * here, as we have to ensure that any dirty inode that we
> - * can't get the flush lock on is attached to the buffer.
> + * here to ensure dirty inodes attached to the buffer remain in
> + * the flushing state while we mark them stale.
> + *
> * If we scan the in-memory inodes first, then buffer IO can
> * complete before we get a lock on it, and hence we may fail
> * to mark all the active inodes on the buffer stale.
> @@ -3443,7 +3432,7 @@ xfs_iflush(
> int error;
>
> ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL|XFS_ILOCK_SHARED));
> - ASSERT(xfs_isiflocked(ip));
> + ASSERT(xfs_iflags_test(ip, XFS_IFLUSHING));
> ASSERT(ip->i_df.if_format != XFS_DINODE_FMT_BTREE ||
> ip->i_df.if_nextents > XFS_IFORK_MAXEXT(ip, XFS_DATA_FORK));
> ASSERT(iip->ili_item.li_buf == bp);
> @@ -3613,7 +3602,7 @@ xfs_iflush_cluster(
> /*
> * Quick and dirty check to avoid locks if possible.
> */
> - if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK))
> + if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLUSHING))
> continue;
> if (xfs_ipincount(ip))
> continue;
> @@ -3627,7 +3616,7 @@ xfs_iflush_cluster(
> */
> spin_lock(&ip->i_flags_lock);
> ASSERT(!__xfs_iflags_test(ip, XFS_ISTALE));
> - if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLOCK)) {
> + if (__xfs_iflags_test(ip, XFS_IRECLAIM | XFS_IFLUSHING)) {
> spin_unlock(&ip->i_flags_lock);
> continue;
> }
> @@ -3635,23 +3624,16 @@ xfs_iflush_cluster(
> /*
> * ILOCK will pin the inode against reclaim and prevent
> * concurrent transactions modifying the inode while we are
> - * flushing the inode.
> + * flushing the inode. If we get the lock, set the flushing
> + * state before we drop the i_flags_lock.
> */
> if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED)) {
> spin_unlock(&ip->i_flags_lock);
> continue;
> }
> + __xfs_iflags_set(ip, XFS_IFLUSHING);
> 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;
> - }
> -
> /*
> * Abort flushing this inode if we are shut down because the
> * inode may not currently be in the AIL. This can occur when
> @@ -3661,7 +3643,6 @@ xfs_iflush_cluster(
> */
> 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;
> @@ -3670,7 +3651,7 @@ xfs_iflush_cluster(
>
> /* don't block waiting on a log force to unpin dirty inodes */
> if (xfs_ipincount(ip)) {
> - xfs_ifunlock(ip);
> + xfs_iflags_clear(ip, XFS_IFLUSHING);
> xfs_iunlock(ip, XFS_ILOCK_SHARED);
> continue;
> }
> @@ -3678,7 +3659,7 @@ xfs_iflush_cluster(
> if (!xfs_inode_clean(ip))
> error = xfs_iflush(ip, bp);
> else
> - xfs_ifunlock(ip);
> + xfs_iflags_clear(ip, XFS_IFLUSHING);
> xfs_iunlock(ip, XFS_ILOCK_SHARED);
> if (error)
> break;
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index e9a8bb184d1f..5ea962c6cf98 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -211,8 +211,7 @@ static inline bool xfs_inode_has_cow_data(struct xfs_inode *ip)
> #define XFS_INEW (1 << __XFS_INEW_BIT)
> #define XFS_ITRUNCATED (1 << 5) /* truncated down so flush-on-close */
> #define XFS_IDIRTY_RELEASE (1 << 6) /* dirty release already seen */
> -#define __XFS_IFLOCK_BIT 7 /* inode is being flushed right now */
> -#define XFS_IFLOCK (1 << __XFS_IFLOCK_BIT)
> +#define XFS_IFLUSHING (1 << 7) /* inode is being flushed */
> #define __XFS_IPINNED_BIT 8 /* wakeup key for zero pin count */
> #define XFS_IPINNED (1 << __XFS_IPINNED_BIT)
> #define XFS_IEOFBLOCKS (1 << 9) /* has the preallocblocks tag set */
> @@ -233,36 +232,6 @@ static inline bool xfs_inode_has_cow_data(struct xfs_inode *ip)
> (XFS_IRECLAIMABLE | XFS_IRECLAIM | \
> XFS_IDIRTY_RELEASE | XFS_ITRUNCATED)
>
> -/*
> - * Synchronize processes attempting to flush the in-core inode back to disk.
> - */
> -
> -static inline int xfs_isiflocked(struct xfs_inode *ip)
> -{
> - return xfs_iflags_test(ip, XFS_IFLOCK);
> -}
> -
> -extern void __xfs_iflock(struct xfs_inode *ip);
> -
> -static inline int xfs_iflock_nowait(struct xfs_inode *ip)
> -{
> - return !xfs_iflags_test_and_set(ip, XFS_IFLOCK);
> -}
> -
> -static inline void xfs_iflock(struct xfs_inode *ip)
> -{
> - if (!xfs_iflock_nowait(ip))
> - __xfs_iflock(ip);
> -}
> -
> -static inline void xfs_ifunlock(struct xfs_inode *ip)
> -{
> - ASSERT(xfs_isiflocked(ip));
> - xfs_iflags_clear(ip, XFS_IFLOCK);
> - smp_mb();
> - wake_up_bit(&ip->i_flags, __XFS_IFLOCK_BIT);
> -}
> -
> /*
> * Flags for inode locking.
> * Bit ranges: 1<<1 - 1<<16-1 -- iolock/ilock modes (bitfield)
> diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
> index 6c65938cee1c..099ae8ee7908 100644
> --- a/fs/xfs/xfs_inode_item.c
> +++ b/fs/xfs/xfs_inode_item.c
> @@ -491,8 +491,7 @@ xfs_inode_item_push(
> (ip->i_flags & XFS_ISTALE))
> return XFS_ITEM_PINNED;
>
> - /* If the inode is already flush locked, we're already flushing. */
> - if (xfs_isiflocked(ip))
> + if (xfs_iflags_test(ip, XFS_IFLUSHING))
> return XFS_ITEM_FLUSHING;
>
> if (!xfs_buf_trylock(bp))
> @@ -703,7 +702,7 @@ xfs_iflush_finish(
> iip->ili_last_fields = 0;
> iip->ili_flush_lsn = 0;
> spin_unlock(&iip->ili_lock);
> - xfs_ifunlock(iip->ili_inode);
> + xfs_iflags_clear(iip->ili_inode, XFS_IFLUSHING);
> if (drop_buffer)
> xfs_buf_rele(bp);
> }
> @@ -711,8 +710,8 @@ xfs_iflush_finish(
>
> /*
> * Inode buffer IO completion routine. It is responsible for removing inodes
> - * attached to the buffer from the AIL if they have not been re-logged, as well
> - * as completing the flush and unlocking the inode.
> + * attached to the buffer from the AIL if they have not been re-logged and
> + * completing the inode flush.
> */
> void
> xfs_iflush_done(
> @@ -755,10 +754,10 @@ xfs_iflush_done(
> }
>
> /*
> - * This is the inode flushing abort routine. It is called from xfs_iflush when
> + * This is the inode flushing abort routine. It is called when
> * the filesystem is shutting down to clean up the inode state. It is
> * responsible for removing the inode item from the AIL if it has not been
> - * re-logged, and unlocking the inode's flush lock.
> + * re-logged and clearing the inode's flush state.
> */
> void
> xfs_iflush_abort(
> @@ -790,7 +789,7 @@ xfs_iflush_abort(
> list_del_init(&iip->ili_item.li_bio_list);
> spin_unlock(&iip->ili_lock);
> }
> - xfs_ifunlock(ip);
> + xfs_iflags_clear(ip, XFS_IFLUSHING);
> if (bp)
> xfs_buf_rele(bp);
> }
> diff --git a/fs/xfs/xfs_inode_item.h b/fs/xfs/xfs_inode_item.h
> index 048b5e7dee90..23a7b4928727 100644
> --- a/fs/xfs/xfs_inode_item.h
> +++ b/fs/xfs/xfs_inode_item.h
> @@ -25,8 +25,8 @@ struct xfs_inode_log_item {
> *
> * We need atomic changes between inode dirtying, inode flushing and
> * inode completion, but these all hold different combinations of
> - * ILOCK and iflock and hence we need some other method of serialising
> - * updates to the flush state.
> + * ILOCK and IFLUSHING and hence we need some other method of
> + * serialising updates to the flush state.
> */
> spinlock_t ili_lock; /* flush state lock */
> unsigned int ili_last_fields; /* fields when flushed */
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index c8ae49a1e99c..bbfd1d5b1c04 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -1059,11 +1059,12 @@ xfs_unmountfs(
> * We can potentially deadlock here if we have an inode cluster
> * that has been freed has its buffer still pinned in memory because
> * the transaction is still sitting in a iclog. The stale inodes
> - * on that buffer will have their flush locks held until the
> - * transaction hits the disk and the callbacks run. the inode
> - * flush takes the flush lock unconditionally and with nothing to
> - * push out the iclog we will never get that unlocked. hence we
> - * need to force the log first.
> + * on that buffer will be pinned to the buffer until the
> + * transaction hits the disk and the callbacks run. Pushing the AIL will
> + * skip the stale inodes and may never see the pinned buffer, so
> + * nothing will push out the iclog and unpin the buffer. Hence we
> + * need to force the log here to ensure all items are flushed into the
> + * AIL before we go any further.
> */
> xfs_log_force(mp, XFS_LOG_SYNC);
>
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 71ac6c1cdc36..68ec8db12cc7 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -654,11 +654,11 @@ xfs_fs_destroy_inode(
> ASSERT_ALWAYS(!xfs_iflags_test(ip, XFS_IRECLAIM));
>
> /*
> - * We always use background reclaim here because even if the
> - * inode is clean, it still may be under IO and hence we have
> - * to take the flush lock. The background reclaim path handles
> - * this more efficiently than we can here, so simply let background
> - * reclaim tear down all inodes.
> + * We always use background reclaim here because even if the inode is
> + * clean, it still may be under IO and hence we have wait for IO
> + * completion to occur before we can reclaim the inode. The background
> + * reclaim path handles this more efficiently than we can here, so
> + * simply let background reclaim tear down all inodes.
> */
> xfs_inode_set_reclaim_tag(ip);
> }
> --
> 2.26.2.761.g0e0b3e54be
>