From 23420d05e67d23728e116321c4afe084ebfa6427 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Sat, 29 Sep 2018 13:45:02 +1000 Subject: xfs: clean up xfs_trans_brelse() xfs_trans_brelse() is a bit of a historical mess, similar to xfs_buf_item_unlock(). It is unnecessarily verbose, has snippets of commented out code, inconsistency with regard to stale items, etc. Clean up xfs_trans_brelse() to use similar logic and flow as xfs_buf_item_unlock() with regard to bli reference count handling. This patch makes no functional changes, but facilitates further refactoring of the common bli reference count handling code. Signed-off-by: Brian Foster Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner --- fs/xfs/xfs_trans_buf.c | 110 ++++++++++++++++++------------------------------- 1 file changed, 39 insertions(+), 71 deletions(-) (limited to 'fs/xfs/xfs_trans_buf.c') diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c index 15919f67a88f..7498f87ceed3 100644 --- a/fs/xfs/xfs_trans_buf.c +++ b/fs/xfs/xfs_trans_buf.c @@ -322,49 +322,40 @@ xfs_trans_read_buf_map( } /* - * Release the buffer bp which was previously acquired with one of the - * xfs_trans_... buffer allocation routines if the buffer has not - * been modified within this transaction. If the buffer is modified - * within this transaction, do decrement the recursion count but do - * not release the buffer even if the count goes to 0. If the buffer is not - * modified within the transaction, decrement the recursion count and - * release the buffer if the recursion count goes to 0. + * Release a buffer previously joined to the transaction. If the buffer is + * modified within this transaction, decrement the recursion count but do not + * release the buffer even if the count goes to 0. If the buffer is not modified + * within the transaction, decrement the recursion count and release the buffer + * if the recursion count goes to 0. * - * If the buffer is to be released and it was not modified before - * this transaction began, then free the buf_log_item associated with it. + * If the buffer is to be released and it was not already dirty before this + * transaction began, then also free the buf_log_item associated with it. * - * If the transaction pointer is NULL, make this just a normal - * brelse() call. + * If the transaction pointer is NULL, this is a normal xfs_buf_relse() call. */ void xfs_trans_brelse( - xfs_trans_t *tp, - xfs_buf_t *bp) + struct xfs_trans *tp, + struct xfs_buf *bp) { - struct xfs_buf_log_item *bip; - int freed; + struct xfs_buf_log_item *bip = bp->b_log_item; + bool freed; + bool dirty; - /* - * Default to a normal brelse() call if the tp is NULL. - */ - if (tp == NULL) { - ASSERT(bp->b_transp == NULL); + ASSERT(bp->b_transp == tp); + + if (!tp) { xfs_buf_relse(bp); return; } - ASSERT(bp->b_transp == tp); - bip = bp->b_log_item; + trace_xfs_trans_brelse(bip); ASSERT(bip->bli_item.li_type == XFS_LI_BUF); - ASSERT(!(bip->bli_flags & XFS_BLI_STALE)); - ASSERT(!(bip->__bli_format.blf_flags & XFS_BLF_CANCEL)); ASSERT(atomic_read(&bip->bli_refcount) > 0); - trace_xfs_trans_brelse(bip); - /* - * If the release is just for a recursive lock, - * then decrement the count and return. + * If the release is for a recursive lookup, then decrement the count + * and return. */ if (bip->bli_recur > 0) { bip->bli_recur--; @@ -372,63 +363,40 @@ xfs_trans_brelse( } /* - * If the buffer is dirty within this transaction, we can't + * If the buffer is invalidated or dirty in this transaction, we can't * release it until we commit. */ if (test_bit(XFS_LI_DIRTY, &bip->bli_item.li_flags)) return; - - /* - * If the buffer has been invalidated, then we can't release - * it until the transaction commits to disk unless it is re-dirtied - * as part of this transaction. This prevents us from pulling - * the item from the AIL before we should. - */ if (bip->bli_flags & XFS_BLI_STALE) return; - ASSERT(!(bip->bli_flags & XFS_BLI_LOGGED)); - /* - * Free up the log item descriptor tracking the released item. + * Unlink the log item from the transaction and clear the hold flag, if + * set. We wouldn't want the next user of the buffer to get confused. */ + ASSERT(!(bip->bli_flags & XFS_BLI_LOGGED)); xfs_trans_del_item(&bip->bli_item); + bip->bli_flags &= ~XFS_BLI_HOLD; /* - * Clear the hold flag in the buf log item if it is set. - * We wouldn't want the next user of the buffer to - * get confused. - */ - if (bip->bli_flags & XFS_BLI_HOLD) { - bip->bli_flags &= ~XFS_BLI_HOLD; - } - - /* - * Drop our reference to the buf log item. + * Drop the reference to the bli. At this point, the bli must be either + * freed or dirty (or both). If freed, there are a couple cases where we + * are responsible to free the item. If the bli is clean, we're the last + * user of it. If the fs has shut down, the bli may be dirty and AIL + * resident, but won't ever be written back. We therefore may also need + * to remove it from the AIL before freeing it. */ freed = atomic_dec_and_test(&bip->bli_refcount); - - /* - * If the buf item is not tracking data in the log, then we must free it - * before releasing the buffer back to the free pool. - * - * If the fs has shutdown and we dropped the last reference, it may fall - * on us to release a (possibly dirty) bli if it never made it to the - * AIL (e.g., the aborted unpin already happened and didn't release it - * due to our reference). Since we're already shutdown and need - * ail_lock, just force remove from the AIL and release the bli here. - */ - if (XFS_FORCED_SHUTDOWN(tp->t_mountp) && freed) { - xfs_trans_ail_remove(&bip->bli_item, SHUTDOWN_LOG_IO_ERROR); - xfs_buf_item_relse(bp); - } else if (!(bip->bli_flags & XFS_BLI_DIRTY)) { -/*** - ASSERT(bp->b_pincount == 0); -***/ - ASSERT(atomic_read(&bip->bli_refcount) == 0); - ASSERT(!test_bit(XFS_LI_IN_AIL, &bip->bli_item.li_flags)); - ASSERT(!(bip->bli_flags & XFS_BLI_INODE_ALLOC_BUF)); - xfs_buf_item_relse(bp); + dirty = bip->bli_flags & XFS_BLI_DIRTY; + ASSERT(freed || dirty); + if (freed) { + bool abort = XFS_FORCED_SHUTDOWN(tp->t_mountp); + ASSERT(abort || !test_bit(XFS_LI_IN_AIL, &bip->bli_item.li_flags)); + if (abort) + xfs_trans_ail_remove(&bip->bli_item, SHUTDOWN_LOG_IO_ERROR); + if (!dirty || abort) + xfs_buf_item_relse(bp); } bp->b_transp = NULL; -- cgit v1.2.3-70-g09d2 From 95808459b110f16b50f03a70ecfa72bb14bd8a96 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Sat, 29 Sep 2018 13:45:26 +1000 Subject: xfs: refactor xfs_buf_log_item reference count handling The xfs_buf_log_item structure has a reference counter with slightly tricky semantics. In the common case, a buffer is logged and committed in a transaction, committed to the on-disk log (added to the AIL) and then finally written back and removed from the AIL. The bli refcount covers two potentially overlapping timeframes: 1. the bli is held in an active transaction 2. the bli is pinned by the log The caveat to this approach is that the reference counter does not purely dictate the lifetime of the bli. IOW, when a dirty buffer is physically logged and unpinned, the bli refcount may go to zero as the log item is inserted into the AIL. Only once the buffer is written back can the bli finally be freed. The above semantics means that it is not enough for the various refcount decrementing contexts to release the bli on decrement to zero. xfs_trans_brelse(), transaction commit (->iop_unlock()) and unpin (->iop_unpin()) must all drop the associated reference and make additional checks to determine if the current context is responsible for freeing the item. For example, if a transaction holds but does not dirty a particular bli, the commit may drop the refcount to zero. If the bli itself is clean, it is also not AIL resident and must be freed at this time. The same is true for xfs_trans_brelse(). If the transaction dirties a bli and then aborts or an unpin results in an abort due to a log I/O error, the last reference count holder is expected to explicitly remove the item from the AIL and release it (since an abort means filesystem shutdown and metadata writeback will never occur). This leads to fairly complex checks being replicated in a few different places. Since ->iop_unlock() and xfs_trans_brelse() are nearly identical, refactor the logic into a common helper that implements and documents the semantics in one place. This patch does not change behavior. Signed-off-by: Brian Foster Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner --- fs/xfs/xfs_buf_item.c | 90 +++++++++++++++++++++++++++++--------------------- fs/xfs/xfs_buf_item.h | 1 + fs/xfs/xfs_trans_buf.c | 23 ++----------- 3 files changed, 56 insertions(+), 58 deletions(-) (limited to 'fs/xfs/xfs_trans_buf.c') diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c index 42fce70b474d..12d8455bfbb2 100644 --- a/fs/xfs/xfs_buf_item.c +++ b/fs/xfs/xfs_buf_item.c @@ -531,6 +531,49 @@ xfs_buf_item_push( return rval; } +/* + * Drop the buffer log item refcount and take appropriate action. This helper + * determines whether the bli must be freed or not, since a decrement to zero + * does not necessarily mean the bli is unused. + * + * Return true if the bli is freed, false otherwise. + */ +bool +xfs_buf_item_put( + struct xfs_buf_log_item *bip) +{ + struct xfs_log_item *lip = &bip->bli_item; + bool aborted; + bool dirty; + + /* drop the bli ref and return if it wasn't the last one */ + if (!atomic_dec_and_test(&bip->bli_refcount)) + return false; + + /* + * We dropped the last ref and must free the item if clean or aborted. + * If the bli is dirty and non-aborted, the buffer was clean in the + * transaction but still awaiting writeback from previous changes. In + * that case, the bli is freed on buffer writeback completion. + */ + aborted = test_bit(XFS_LI_ABORTED, &lip->li_flags) || + XFS_FORCED_SHUTDOWN(lip->li_mountp); + dirty = bip->bli_flags & XFS_BLI_DIRTY; + if (dirty && !aborted) + return false; + + /* + * The bli is aborted or clean. An aborted item may be in the AIL + * regardless of dirty state. For example, consider an aborted + * transaction that invalidated a dirty bli and cleared the dirty + * state. + */ + if (aborted) + xfs_trans_ail_remove(lip, SHUTDOWN_LOG_IO_ERROR); + xfs_buf_item_relse(bip->bli_buf); + return true; +} + /* * Release the buffer associated with the buf log item. If there is no dirty * logged data associated with the buffer recorded in the buf log item, then @@ -556,13 +599,12 @@ xfs_buf_item_unlock( { struct xfs_buf_log_item *bip = BUF_ITEM(lip); struct xfs_buf *bp = bip->bli_buf; - bool freed; - bool aborted; + bool released; bool hold = bip->bli_flags & XFS_BLI_HOLD; - bool dirty = bip->bli_flags & XFS_BLI_DIRTY; bool stale = bip->bli_flags & XFS_BLI_STALE; #if defined(DEBUG) || defined(XFS_WARN) bool ordered = bip->bli_flags & XFS_BLI_ORDERED; + bool dirty = bip->bli_flags & XFS_BLI_DIRTY; #endif trace_xfs_buf_item_unlock(bip); @@ -575,8 +617,6 @@ xfs_buf_item_unlock( (ordered && dirty && !xfs_buf_item_dirty_format(bip))); ASSERT(!stale || (bip->__bli_format.blf_flags & XFS_BLF_CANCEL)); - aborted = test_bit(XFS_LI_ABORTED, &lip->li_flags); - /* * Clear the buffer's association with this transaction and * per-transaction state from the bli, which has been copied above. @@ -585,40 +625,16 @@ xfs_buf_item_unlock( bip->bli_flags &= ~(XFS_BLI_LOGGED | XFS_BLI_HOLD | XFS_BLI_ORDERED); /* - * Drop the transaction's bli reference and deal with the item if we had - * the last one. We must free the item if clean or aborted since it - * wasn't pinned by the log and this is the last chance to do so. If the - * bli is freed and dirty (but non-aborted), the buffer was not dirty in - * this transaction but modified by a previous one and still awaiting - * writeback. In that case, the bli is freed on buffer writeback - * completion. + * Unref the item and unlock the buffer unless held or stale. Stale + * buffers remain locked until final unpin unless the bli is freed by + * the unref call. The latter implies shutdown because buffer + * invalidation dirties the bli and transaction. */ - freed = atomic_dec_and_test(&bip->bli_refcount); - if (freed) { - ASSERT(!aborted || XFS_FORCED_SHUTDOWN(lip->li_mountp)); - /* - * An aborted item may be in the AIL regardless of dirty state. - * For example, consider an aborted transaction that invalidated - * a dirty bli and cleared the dirty state. - */ - if (aborted) - xfs_trans_ail_remove(lip, SHUTDOWN_LOG_IO_ERROR); - if (aborted || !dirty) - xfs_buf_item_relse(bp); - } else if (stale) { - /* - * Stale buffers remain locked until final unpin unless the bli - * was freed in the branch above. A freed stale bli implies an - * abort because buffer invalidation dirties the bli and - * transaction. - */ - ASSERT(!freed); + released = xfs_buf_item_put(bip); + if (hold || (stale && !released)) return; - } - ASSERT(!stale || (aborted && freed)); - - if (!hold) - xfs_buf_relse(bp); + ASSERT(!stale || test_bit(XFS_LI_ABORTED, &lip->li_flags)); + xfs_buf_relse(bp); } /* diff --git a/fs/xfs/xfs_buf_item.h b/fs/xfs/xfs_buf_item.h index 3f7d7b72e7e6..90f65f891fab 100644 --- a/fs/xfs/xfs_buf_item.h +++ b/fs/xfs/xfs_buf_item.h @@ -51,6 +51,7 @@ struct xfs_buf_log_item { int xfs_buf_item_init(struct xfs_buf *, struct xfs_mount *); void xfs_buf_item_relse(struct xfs_buf *); +bool xfs_buf_item_put(struct xfs_buf_log_item *); void xfs_buf_item_log(struct xfs_buf_log_item *, uint, uint); bool xfs_buf_item_dirty_format(struct xfs_buf_log_item *); void xfs_buf_attach_iodone(struct xfs_buf *, diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c index 7498f87ceed3..286a287ac57a 100644 --- a/fs/xfs/xfs_trans_buf.c +++ b/fs/xfs/xfs_trans_buf.c @@ -339,8 +339,6 @@ xfs_trans_brelse( struct xfs_buf *bp) { struct xfs_buf_log_item *bip = bp->b_log_item; - bool freed; - bool dirty; ASSERT(bp->b_transp == tp); @@ -379,25 +377,8 @@ xfs_trans_brelse( xfs_trans_del_item(&bip->bli_item); bip->bli_flags &= ~XFS_BLI_HOLD; - /* - * Drop the reference to the bli. At this point, the bli must be either - * freed or dirty (or both). If freed, there are a couple cases where we - * are responsible to free the item. If the bli is clean, we're the last - * user of it. If the fs has shut down, the bli may be dirty and AIL - * resident, but won't ever be written back. We therefore may also need - * to remove it from the AIL before freeing it. - */ - freed = atomic_dec_and_test(&bip->bli_refcount); - dirty = bip->bli_flags & XFS_BLI_DIRTY; - ASSERT(freed || dirty); - if (freed) { - bool abort = XFS_FORCED_SHUTDOWN(tp->t_mountp); - ASSERT(abort || !test_bit(XFS_LI_IN_AIL, &bip->bli_item.li_flags)); - if (abort) - xfs_trans_ail_remove(&bip->bli_item, SHUTDOWN_LOG_IO_ERROR); - if (!dirty || abort) - xfs_buf_item_relse(bp); - } + /* drop the reference to the bli */ + xfs_buf_item_put(bip); bp->b_transp = NULL; xfs_buf_relse(bp); -- cgit v1.2.3-70-g09d2