[XFS] Replace custom AIL linked-list code with struct list_head

Replace the xfs_ail_entry_t with a struct list_head and clean the
surrounding code up. Also fixes a livelock in xfs_trans_first_push_ail()
by terminating the loop at the head of the list correctly.

SGI-PV: 978682
SGI-Modid: xfs-linux-melb:xfs-kern:30636a

Signed-off-by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

3 files changed, 62 insertions, 96 deletions

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 7b37fa00929..77b39f66cea 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -220,7 +220,7 @@ extern void	xfs_icsb_sync_counters_flags(struct xfs_mount *, int);
 #endif
 
 typedef struct xfs_ail {
-        xfs_ail_entry_t         xa_ail;
+        struct list_head        xa_ail;
         uint                    xa_gen;
         struct task_struct      *xa_task;
         xfs_lsn_t               xa_target;
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index b5effce0008..0804207c739 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -113,13 +113,8 @@ struct xfs_mount;
 struct xfs_trans;
 struct xfs_dquot_acct;
 
-typedef struct xfs_ail_entry {
-        struct xfs_log_item     *ail_forw;      /* AIL forw pointer */
-        struct xfs_log_item     *ail_back;      /* AIL back pointer */
-} xfs_ail_entry_t;
-
 typedef struct xfs_log_item {
-        xfs_ail_entry_t                 li_ail;         /* AIL pointers */
+        struct list_head                li_ail;         /* AIL pointers */
         xfs_lsn_t                       li_lsn;         /* last on-disk lsn */
         struct xfs_log_item_desc        *li_desc;       /* ptr to current desc*/
         struct xfs_mount                *li_mountp;     /* ptr to fs mount */
diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 76d470d8a1e..13235ae9a58 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -28,13 +28,13 @@
 #include "xfs_trans_priv.h"
 #include "xfs_error.h"
 
-STATIC void xfs_ail_insert(xfs_ail_entry_t *, xfs_log_item_t *);
-STATIC xfs_log_item_t * xfs_ail_delete(xfs_ail_entry_t *, xfs_log_item_t *);
-STATIC xfs_log_item_t * xfs_ail_min(xfs_ail_entry_t *);
-STATIC xfs_log_item_t * xfs_ail_next(xfs_ail_entry_t *, xfs_log_item_t *);
+STATIC void xfs_ail_insert(xfs_ail_t *, xfs_log_item_t *);
+STATIC xfs_log_item_t * xfs_ail_delete(xfs_ail_t *, xfs_log_item_t *);
+STATIC xfs_log_item_t * xfs_ail_min(xfs_ail_t *);
+STATIC xfs_log_item_t * xfs_ail_next(xfs_ail_t *, xfs_log_item_t *);
 
 #ifdef DEBUG
-STATIC void xfs_ail_check(xfs_ail_entry_t *, xfs_log_item_t *);
+STATIC void xfs_ail_check(xfs_ail_t *, xfs_log_item_t *);
 #else
 #define xfs_ail_check(a,l)
 #endif /* DEBUG */
@@ -57,7 +57,7 @@ xfs_trans_tail_ail(
         xfs_log_item_t  *lip;
 
         spin_lock(&mp->m_ail_lock);
-        lip = xfs_ail_min(&(mp->m_ail.xa_ail));
+        lip = xfs_ail_min(&mp->m_ail);
         if (lip == NULL) {
                 lsn = (xfs_lsn_t)0;
         } else {
@@ -91,7 +91,7 @@ xfs_trans_push_ail(
 {
         xfs_log_item_t          *lip;
 
-        lip = xfs_ail_min(&mp->m_ail.xa_ail);
+        lip = xfs_ail_min(&mp->m_ail);
         if (lip && !XFS_FORCED_SHUTDOWN(mp)) {
                 if (XFS_LSN_CMP(threshold_lsn, mp->m_ail.xa_target) > 0)
                         xfsaild_wakeup(mp, threshold_lsn);
@@ -111,15 +111,17 @@ xfs_trans_first_push_ail(
 {
         xfs_log_item_t  *lip;
 
-        lip = xfs_ail_min(&(mp->m_ail.xa_ail));
+        lip = xfs_ail_min(&mp->m_ail);
         *gen = (int)mp->m_ail.xa_gen;
         if (lsn == 0)
                 return lip;
 
-        while (lip && (XFS_LSN_CMP(lip->li_lsn, lsn) < 0))
-                lip = lip->li_ail.ail_forw;
+        list_for_each_entry(lip, &mp->m_ail.xa_ail, li_ail) {
+                if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0)
+                        return lip;
+        }
 
-        return lip;
+        return NULL;
 }
 
 /*
@@ -329,7 +331,7 @@ xfs_trans_unlocked_item(
          * the call to xfs_log_move_tail() doesn't do anything if there's
          * not enough free space to wake people up so we're safe calling it.
          */
-        min_lip = xfs_ail_min(&mp->m_ail.xa_ail);
+        min_lip = xfs_ail_min(&mp->m_ail);
 
         if (min_lip == lip)
                 xfs_log_move_tail(mp, 1);
@@ -357,15 +359,13 @@ xfs_trans_update_ail(
         xfs_log_item_t  *lip,
         xfs_lsn_t       lsn) __releases(mp->m_ail_lock)
 {
-        xfs_ail_entry_t         *ailp;
         xfs_log_item_t          *dlip=NULL;
         xfs_log_item_t          *mlip;  /* ptr to minimum lip */
 
-        ailp = &(mp->m_ail.xa_ail);
-        mlip = xfs_ail_min(ailp);
+        mlip = xfs_ail_min(&mp->m_ail);
 
         if (lip->li_flags & XFS_LI_IN_AIL) {
-                dlip = xfs_ail_delete(ailp, lip);
+                dlip = xfs_ail_delete(&mp->m_ail, lip);
                 ASSERT(dlip == lip);
         } else {
                 lip->li_flags |= XFS_LI_IN_AIL;
@@ -373,11 +373,11 @@ xfs_trans_update_ail(
 
         lip->li_lsn = lsn;
 
-        xfs_ail_insert(ailp, lip);
+        xfs_ail_insert(&mp->m_ail, lip);
         mp->m_ail.xa_gen++;
 
         if (mlip == dlip) {
-                mlip = xfs_ail_min(&(mp->m_ail.xa_ail));
+                mlip = xfs_ail_min(&mp->m_ail);
                 spin_unlock(&mp->m_ail_lock);
                 xfs_log_move_tail(mp, mlip->li_lsn);
         } else {
@@ -407,14 +407,12 @@ xfs_trans_delete_ail(
         xfs_mount_t     *mp,
         xfs_log_item_t  *lip) __releases(mp->m_ail_lock)
 {
-        xfs_ail_entry_t         *ailp;
         xfs_log_item_t          *dlip;
         xfs_log_item_t          *mlip;
 
         if (lip->li_flags & XFS_LI_IN_AIL) {
-                ailp = &(mp->m_ail.xa_ail);
-                mlip = xfs_ail_min(ailp);
-                dlip = xfs_ail_delete(ailp, lip);
+                mlip = xfs_ail_min(&mp->m_ail);
+                dlip = xfs_ail_delete(&mp->m_ail, lip);
                 ASSERT(dlip == lip);
 
 
@@ -423,7 +421,7 @@ xfs_trans_delete_ail(
                 mp->m_ail.xa_gen++;
 
                 if (mlip == dlip) {
-                        mlip = xfs_ail_min(&(mp->m_ail.xa_ail));
+                        mlip = xfs_ail_min(&mp->m_ail);
                         spin_unlock(&mp->m_ail_lock);
                         xfs_log_move_tail(mp, (mlip ? mlip->li_lsn : 0));
                 } else {
@@ -461,7 +459,7 @@ xfs_trans_first_ail(
 {
         xfs_log_item_t  *lip;
 
-        lip = xfs_ail_min(&(mp->m_ail.xa_ail));
+        lip = xfs_ail_min(&mp->m_ail);
         *gen = (int)mp->m_ail.xa_gen;
 
         return lip;
@@ -485,9 +483,9 @@ xfs_trans_next_ail(
 
         ASSERT(mp && lip && gen);
         if (mp->m_ail.xa_gen == *gen) {
-                nlip = xfs_ail_next(&(mp->m_ail.xa_ail), lip);
+                nlip = xfs_ail_next(&mp->m_ail, lip);
         } else {
-                nlip = xfs_ail_min(&(mp->m_ail).xa_ail);
+                nlip = xfs_ail_min(&mp->m_ail);
                 *gen = (int)mp->m_ail.xa_gen;
                 if (restarts != NULL) {
                         XFS_STATS_INC(xs_push_ail_restarts);
@@ -517,8 +515,7 @@ int
 xfs_trans_ail_init(
         xfs_mount_t     *mp)
 {
-        mp->m_ail.xa_ail.ail_forw = (xfs_log_item_t*)&mp->m_ail.xa_ail;
-        mp->m_ail.xa_ail.ail_back = (xfs_log_item_t*)&mp->m_ail.xa_ail;
+        INIT_LIST_HEAD(&mp->m_ail.xa_ail);
         return xfsaild_start(mp);
 }
 
@@ -537,7 +534,7 @@ xfs_trans_ail_destroy(
  */
 STATIC void
 xfs_ail_insert(
-        xfs_ail_entry_t *base,
+        xfs_ail_t       *ailp,
         xfs_log_item_t  *lip)
 /* ARGSUSED */
 {
@@ -546,27 +543,22 @@ xfs_ail_insert(
         /*
          * If the list is empty, just insert the item.
          */
-        if (base->ail_back == (xfs_log_item_t*)base) {
-                base->ail_forw = lip;
-                base->ail_back = lip;
-                lip->li_ail.ail_forw = (xfs_log_item_t*)base;
-                lip->li_ail.ail_back = (xfs_log_item_t*)base;
+        if (list_empty(&ailp->xa_ail)) {
+                list_add(&lip->li_ail, &ailp->xa_ail);
                 return;
         }
 
-        next_lip = base->ail_back;
-        while ((next_lip != (xfs_log_item_t*)base) &&
-               (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) > 0)) {
-                next_lip = next_lip->li_ail.ail_back;
+        list_for_each_entry_reverse(next_lip, &ailp->xa_ail, li_ail) {
+                if (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0)
+                        break;
         }
-        ASSERT((next_lip == (xfs_log_item_t*)base) ||
+
+        ASSERT((&next_lip->li_ail == &ailp->xa_ail) ||
                (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0));
-        lip->li_ail.ail_forw = next_lip->li_ail.ail_forw;
-        lip->li_ail.ail_back = next_lip;
-        next_lip->li_ail.ail_forw = lip;
-        lip->li_ail.ail_forw->li_ail.ail_back = lip;
 
-        xfs_ail_check(base, lip);
+        list_add(&lip->li_ail, &next_lip->li_ail);
+
+        xfs_ail_check(ailp, lip);
         return;
 }
 
@@ -576,15 +568,13 @@ xfs_ail_insert(
 /*ARGSUSED*/
 STATIC xfs_log_item_t *
 xfs_ail_delete(
-        xfs_ail_entry_t *base,
+        xfs_ail_t       *ailp,
         xfs_log_item_t  *lip)
 /* ARGSUSED */
 {
-        xfs_ail_check(base, lip);
-        lip->li_ail.ail_forw->li_ail.ail_back = lip->li_ail.ail_back;
-        lip->li_ail.ail_back->li_ail.ail_forw = lip->li_ail.ail_forw;
-        lip->li_ail.ail_forw = NULL;
-        lip->li_ail.ail_back = NULL;
+        xfs_ail_check(ailp, lip);
+
+        list_del(&lip->li_ail);
 
         return lip;
 }
@@ -595,14 +585,13 @@ xfs_ail_delete(
  */
 STATIC xfs_log_item_t *
 xfs_ail_min(
-        xfs_ail_entry_t *base)
+        xfs_ail_t       *ailp)
 /* ARGSUSED */
 {
-        register xfs_log_item_t *forw = base->ail_forw;
-        if (forw == (xfs_log_item_t*)base) {
+        if (list_empty(&ailp->xa_ail))
                 return NULL;
-        }
-        return forw;
+
+        return list_first_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
 }
 
 /*
@@ -612,15 +601,14 @@ xfs_ail_min(
  */
 STATIC xfs_log_item_t *
 xfs_ail_next(
-        xfs_ail_entry_t *base,
+        xfs_ail_t       *ailp,
         xfs_log_item_t  *lip)
 /* ARGSUSED */
 {
-        if (lip->li_ail.ail_forw == (xfs_log_item_t*)base) {
+        if (lip->li_ail.next == &ailp->xa_ail)
                 return NULL;
-        }
-        return lip->li_ail.ail_forw;
 
+        return list_first_entry(&lip->li_ail, xfs_log_item_t, li_ail);
 }
 
 #ifdef DEBUG
@@ -629,57 +617,40 @@ xfs_ail_next(
  */
 STATIC void
 xfs_ail_check(
-        xfs_ail_entry_t *base,
+        xfs_ail_t       *ailp,
         xfs_log_item_t  *lip)
 {
         xfs_log_item_t  *prev_lip;
 
-        prev_lip = base->ail_forw;
-        if (prev_lip == (xfs_log_item_t*)base) {
-                /*
-                 * Make sure the pointers are correct when the list
-                 * is empty.
-                 */
-                ASSERT(base->ail_back == (xfs_log_item_t*)base);
+        if (list_empty(&ailp->xa_ail))
                 return;
-        }
 
         /*
          * Check the next and previous entries are valid.
          */
         ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
-        prev_lip = lip->li_ail.ail_back;
-        if (prev_lip != (xfs_log_item_t*)base) {
-                ASSERT(prev_lip->li_ail.ail_forw == lip);
+        prev_lip = list_entry(lip->li_ail.prev, xfs_log_item_t, li_ail);
+        if (&prev_lip->li_ail != &ailp->xa_ail)
                 ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
-        }
-        prev_lip = lip->li_ail.ail_forw;
-        if (prev_lip != (xfs_log_item_t*)base) {
-                ASSERT(prev_lip->li_ail.ail_back == lip);
+
+        prev_lip = list_entry(lip->li_ail.next, xfs_log_item_t, li_ail);
+        if (&prev_lip->li_ail != &ailp->xa_ail)
                 ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) >= 0);
-        }
 
 
 #ifdef XFS_TRANS_DEBUG
         /*
-         * Walk the list checking forward and backward pointers,
-         * lsn ordering, and that every entry has the XFS_LI_IN_AIL
-         * flag set. This is really expensive, so only do it when
-         * specifically debugging the transaction subsystem.
+         * Walk the list checking lsn ordering, and that every entry has the
+         * XFS_LI_IN_AIL flag set. This is really expensive, so only do it
+         * when specifically debugging the transaction subsystem.
          */
-        prev_lip = (xfs_log_item_t*)base;
-        while (lip != (xfs_log_item_t*)base) {
-                if (prev_lip != (xfs_log_item_t*)base) {
-                        ASSERT(prev_lip->li_ail.ail_forw == lip);
+        prev_lip = list_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
+        list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
+                if (&prev_lip->li_ail != &ailp->xa_ail)
                         ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
-                }
-                ASSERT(lip->li_ail.ail_back == prev_lip);
                 ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
                 prev_lip = lip;
-                lip = lip->li_ail.ail_forw;
         }
-        ASSERT(lip == (xfs_log_item_t*)base);
-        ASSERT(base->ail_back == prev_lip);
 #endif /* XFS_TRANS_DEBUG */
 }
 #endif /* DEBUG */