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[PATCH 2/9] xfs: Pull EFI/EFD handling out from under the AIL lock

To: xfs@xxxxxxxxxxx
Subject: [PATCH 2/9] xfs: Pull EFI/EFD handling out from under the AIL lock
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 13 Dec 2010 15:32:16 +1100
In-reply-to: <1292214743-18073-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1292214743-18073-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

EFI/EFD interactions are protected from races by the AIL lock. They
are the only type of log items that require the the AIL lock to
serialise internal state, so they need to be separated from the AIL
lock before we can do bulk insert operations on the AIL.

To acheive this, convert the counter of the number of extents in the
EFI to an atomic so it can be safely manipulated by EFD processing
without locks. Also, convert the EFI state flag manipulations to use
atomic bit operations so no locks are needed to record state
changes. Finally, use the state bits to determine when it is safe to
free the EFI and clean up the code to do this neatly.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_extfree_item.c  |   81 ++++++++++++++++++++++++-------------------
 fs/xfs/xfs_extfree_item.h  |   10 +++---
 fs/xfs/xfs_log_recover.c   |    9 ++---
 fs/xfs/xfs_trans_extfree.c |    8 +++-
 4 files changed, 60 insertions(+), 48 deletions(-)

diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c
index 5997efa..3f9f486 100644
--- a/fs/xfs/xfs_extfree_item.c
+++ b/fs/xfs/xfs_extfree_item.c
@@ -48,6 +48,28 @@ xfs_efi_item_free(
 }
 
 /*
+ * Freeing the efi requires that we remove it from the AIL if it has already
+ * been placed there. However, the EFI may not yet have been placed in the AIL
+ * when called by xfs_efi_release() from EFD processing due to the ordering of
+ * committed vs unpin operations in bulk insert operations. Hence the
+ * test_and_clear_bit(XFS_EFI_COMMITTED) to ensure only the last caller frees
+ * the EFI.
+ */
+STATIC void
+__xfs_efi_release(
+       struct xfs_efi_log_item *efip)
+{
+       struct xfs_ail          *ailp = efip->efi_item.li_ailp;
+
+       if (!test_and_clear_bit(XFS_EFI_COMMITTED, &efip->efi_flags)) {
+               spin_lock(&ailp->xa_lock);
+               /* xfs_trans_ail_delete() drops the AIL lock. */
+               xfs_trans_ail_delete(ailp, (xfs_log_item_t *)efip);
+               xfs_efi_item_free(efip);
+       }
+}
+
+/*
  * This returns the number of iovecs needed to log the given efi item.
  * We only need 1 iovec for an efi item.  It just logs the efi_log_format
  * structure.
@@ -74,7 +96,8 @@ xfs_efi_item_format(
        struct xfs_efi_log_item *efip = EFI_ITEM(lip);
        uint                    size;
 
-       ASSERT(efip->efi_next_extent == efip->efi_format.efi_nextents);
+       ASSERT(atomic_read(&efip->efi_next_extent) ==
+                               efip->efi_format.efi_nextents);
 
        efip->efi_format.efi_type = XFS_LI_EFI;
 
@@ -103,7 +126,8 @@ xfs_efi_item_pin(
  * which the EFI is manipulated during a transaction.  If we are being asked to
  * remove the EFI it's because the transaction has been cancelled and by
  * definition that means the EFI cannot be in the AIL so remove it from the
- * transaction and free it.
+ * transaction and free it.  Otherwise coordinate with xfs_efi_release() (via
+ * XFS_EFI_COMMITTED) to determine who gets to free the EFI.
  */
 STATIC void
 xfs_efi_item_unpin(
@@ -111,17 +135,14 @@ xfs_efi_item_unpin(
        int                     remove)
 {
        struct xfs_efi_log_item *efip = EFI_ITEM(lip);
-       struct xfs_ail          *ailp = lip->li_ailp;
 
-       spin_lock(&ailp->xa_lock);
        if (remove) {
                ASSERT(!(lip->li_flags & XFS_LI_IN_AIL));
                xfs_trans_del_item(lip);
                xfs_efi_item_free(efip);
-       } else {
-               efip->efi_flags |= XFS_EFI_COMMITTED;
+               return;
        }
-       spin_unlock(&ailp->xa_lock);
+       __xfs_efi_release(efip);
 }
 
 /*
@@ -150,16 +171,20 @@ xfs_efi_item_unlock(
 }
 
 /*
- * The EFI is logged only once and cannot be moved in the log, so
- * simply return the lsn at which it's been logged.  The canceled
- * flag is not paid any attention here.  Checking for that is delayed
- * until the EFI is unpinned.
+ * The EFI is logged only once and cannot be moved in the log, so simply return
+ * the lsn at which it's been logged.  For bulk transaction committed
+ * processing, the EFI may be processed but not yet unpinned prior to the EFD
+ * being processed. Set the XFS_EFI_COMMITTED flag so this case can be detected
+ * when processing the EFD.
  */
 STATIC xfs_lsn_t
 xfs_efi_item_committed(
        struct xfs_log_item     *lip,
        xfs_lsn_t               lsn)
 {
+       struct xfs_efi_log_item *efip = EFI_ITEM(lip);
+
+       set_bit(XFS_EFI_COMMITTED, &efip->efi_flags);
        return lsn;
 }
 
@@ -228,6 +253,7 @@ xfs_efi_init(
        xfs_log_item_init(mp, &efip->efi_item, XFS_LI_EFI, &xfs_efi_item_ops);
        efip->efi_format.efi_nextents = nextents;
        efip->efi_format.efi_id = (__psint_t)(void*)efip;
+       atomic_set(&efip->efi_next_extent, 0);
 
        return efip;
 }
@@ -287,37 +313,20 @@ xfs_efi_copy_format(xfs_log_iovec_t *buf, 
xfs_efi_log_format_t *dst_efi_fmt)
 }
 
 /*
- * This is called by the efd item code below to release references to
- * the given efi item.  Each efd calls this with the number of
- * extents that it has logged, and when the sum of these reaches
- * the total number of extents logged by this efi item we can free
- * the efi item.
- *
- * Freeing the efi item requires that we remove it from the AIL.
- * We'll use the AIL lock to protect our counters as well as
- * the removal from the AIL.
+ * This is called by the efd item code below to release references to the given
+ * efi item.  Each efd calls this with the number of extents that it has
+ * logged, and when the sum of these reaches the total number of extents logged
+ * by this efi item we can free the efi item.
  */
 void
 xfs_efi_release(xfs_efi_log_item_t     *efip,
                uint                    nextents)
 {
-       struct xfs_ail          *ailp = efip->efi_item.li_ailp;
-       int                     extents_left;
+       ASSERT(atomic_read(&efip->efi_next_extent) >= nextents);
+       if (!atomic_sub_and_test(nextents, &efip->efi_next_extent))
+               return;
 
-       ASSERT(efip->efi_next_extent > 0);
-       ASSERT(efip->efi_flags & XFS_EFI_COMMITTED);
-
-       spin_lock(&ailp->xa_lock);
-       ASSERT(efip->efi_next_extent >= nextents);
-       efip->efi_next_extent -= nextents;
-       extents_left = efip->efi_next_extent;
-       if (extents_left == 0) {
-               /* xfs_trans_ail_delete() drops the AIL lock. */
-               xfs_trans_ail_delete(ailp, (xfs_log_item_t *)efip);
-               xfs_efi_item_free(efip);
-       } else {
-               spin_unlock(&ailp->xa_lock);
-       }
+       __xfs_efi_release(efip);
 }
 
 static inline struct xfs_efd_log_item *EFD_ITEM(struct xfs_log_item *lip)
diff --git a/fs/xfs/xfs_extfree_item.h b/fs/xfs/xfs_extfree_item.h
index f7834ec..375f68e 100644
--- a/fs/xfs/xfs_extfree_item.h
+++ b/fs/xfs/xfs_extfree_item.h
@@ -111,10 +111,10 @@ typedef struct xfs_efd_log_format_64 {
 #define        XFS_EFI_MAX_FAST_EXTENTS        16
 
 /*
- * Define EFI flags.
+ * Define EFI flag bits. Manipulated by set/clear/test_bit operators.
  */
-#define        XFS_EFI_RECOVERED       0x1
-#define        XFS_EFI_COMMITTED       0x2
+#define        XFS_EFI_RECOVERED       1
+#define        XFS_EFI_COMMITTED       2
 
 /*
  * This is the "extent free intention" log item.  It is used
@@ -124,8 +124,8 @@ typedef struct xfs_efd_log_format_64 {
  */
 typedef struct xfs_efi_log_item {
        xfs_log_item_t          efi_item;
-       uint                    efi_flags;      /* misc flags */
-       uint                    efi_next_extent;
+       atomic_t                efi_next_extent;
+       unsigned long           efi_flags;      /* misc flags */
        xfs_efi_log_format_t    efi_format;
 } xfs_efi_log_item_t;
 
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 966d3f9..e23f7be 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -2717,8 +2717,7 @@ xlog_recover_do_efi_trans(
                xfs_efi_item_free(efip);
                return error;
        }
-       efip->efi_next_extent = efi_formatp->efi_nextents;
-       efip->efi_flags |= XFS_EFI_COMMITTED;
+       atomic_set(&efip->efi_next_extent, efi_formatp->efi_nextents);
 
        spin_lock(&log->l_ailp->xa_lock);
        /*
@@ -3011,7 +3010,7 @@ xlog_recover_process_efi(
        xfs_extent_t            *extp;
        xfs_fsblock_t           startblock_fsb;
 
-       ASSERT(!(efip->efi_flags & XFS_EFI_RECOVERED));
+       ASSERT(!test_bit(XFS_EFI_RECOVERED, &efip->efi_flags));
 
        /*
         * First check the validity of the extents described by the
@@ -3050,7 +3049,7 @@ xlog_recover_process_efi(
                                         extp->ext_len);
        }
 
-       efip->efi_flags |= XFS_EFI_RECOVERED;
+       set_bit(XFS_EFI_RECOVERED, &efip->efi_flags);
        error = xfs_trans_commit(tp, 0);
        return error;
 
@@ -3107,7 +3106,7 @@ xlog_recover_process_efis(
                 * Skip EFIs that we've already processed.
                 */
                efip = (xfs_efi_log_item_t *)lip;
-               if (efip->efi_flags & XFS_EFI_RECOVERED) {
+               if (test_bit(XFS_EFI_RECOVERED, &efip->efi_flags)) {
                        lip = xfs_trans_ail_cursor_next(ailp, &cur);
                        continue;
                }
diff --git a/fs/xfs/xfs_trans_extfree.c b/fs/xfs/xfs_trans_extfree.c
index f783d5e..f7590f5 100644
--- a/fs/xfs/xfs_trans_extfree.c
+++ b/fs/xfs/xfs_trans_extfree.c
@@ -69,12 +69,16 @@ xfs_trans_log_efi_extent(xfs_trans_t                *tp,
        tp->t_flags |= XFS_TRANS_DIRTY;
        efip->efi_item.li_desc->lid_flags |= XFS_LID_DIRTY;
 
-       next_extent = efip->efi_next_extent;
+       /*
+        * atomic_inc_return gives us the value after the increment;
+        * we want to use it as an array index so we need to subtract 1 from
+        * it.
+        */
+       next_extent = atomic_inc_return(&efip->efi_next_extent) - 1;
        ASSERT(next_extent < efip->efi_format.efi_nextents);
        extp = &(efip->efi_format.efi_extents[next_extent]);
        extp->ext_start = start_block;
        extp->ext_len = ext_len;
-       efip->efi_next_extent++;
 }
 
 
-- 
1.7.2.3

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