From d9183105caa926522a4bc8a40e162de7019f1a21 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Sat, 29 Sep 2018 13:44:40 +1000 Subject: xfs: don't unlock invalidated buf on aborted tx commit xfstests generic/388,475 occasionally reproduce assertion failures in xfs_buf_item_unpin() when the final bli reference is dropped on an invalidated buffer and the buffer is not locked as it is expected to be. Invalidated buffers should remain locked on transaction commit until the final unpin, at which point the buffer is removed from the AIL and the bli is freed since stale buffers are not written back. The assert failures are associated with filesystem shutdown, typically due to log I/O errors injected by the test. The problematic situation can occur if the shutdown happens to cause a race between an active transaction that has invalidated a particular buffer and an I/O error on a log buffer that contains the bli associated with the same (now stale) buffer. Both transaction and log contexts acquire a bli reference. If the transaction has already invalidated the buffer by the time the I/O error occurs and ends up aborting due to shutdown, the transaction and log hold the last two references to a stale bli. If the transaction cancel occurs first, it treats the buffer as non-stale due to the aborted state: the bli reference is dropped and the buffer is released/unlocked. The log buffer I/O error handling eventually calls into xfs_buf_item_unpin(), drops the final reference to the bli and treats it as stale. The buffer wasn't left locked by xfs_buf_item_unlock(), however, so the assert fails and the buffer is double unlocked. The latter problem is mitigated by the fact that the fs is shutdown and no further damage is possible. ->iop_unlock() of an invalidated buffer should behave consistently with respect to the bli refcount, regardless of aborted state. If the refcount remains elevated on commit, we know the bli is awaiting an unpin (since it can't be in another transaction) and will be handled appropriately on log buffer completion. If the final bli reference of an invalidated buffer is dropped in ->iop_unlock(), we can assume the transaction has aborted because invalidation implies a dirty transaction. In the non-abort case, the log would have acquired a bli reference in ->iop_pin() and prevented bli release at ->iop_unlock() time. In the abort case the item must be freed and buffer unlocked because it wasn't pinned by the log. Rework xfs_buf_item_unlock() to simplify the currently circuitous and duplicate logic and leave invalidated buffers locked based on bli refcount, regardless of aborted state. This ensures that a pinned, stale buffer is always found locked when eventually unpinned. Signed-off-by: Brian Foster Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner --- fs/xfs/xfs_buf_item.c | 91 ++++++++++++++++++++++++--------------------------- fs/xfs/xfs_trace.h | 1 - 2 files changed, 42 insertions(+), 50 deletions(-) (limited to 'fs') diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c index 1c9d1398980b..42fce70b474d 100644 --- a/fs/xfs/xfs_buf_item.c +++ b/fs/xfs/xfs_buf_item.c @@ -556,73 +556,66 @@ 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 hold = !!(bip->bli_flags & XFS_BLI_HOLD); - bool dirty = !!(bip->bli_flags & XFS_BLI_DIRTY); + 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 ordered = bip->bli_flags & XFS_BLI_ORDERED; #endif - aborted = test_bit(XFS_LI_ABORTED, &lip->li_flags); - - /* Clear the buffer's association with this transaction. */ - bp->b_transp = NULL; - - /* - * The per-transaction state has been copied above so clear it from the - * bli. - */ - bip->bli_flags &= ~(XFS_BLI_LOGGED | XFS_BLI_HOLD | XFS_BLI_ORDERED); - - /* - * If the buf item is marked stale, then don't do anything. We'll - * unlock the buffer and free the buf item when the buffer is unpinned - * for the last time. - */ - if (bip->bli_flags & XFS_BLI_STALE) { - trace_xfs_buf_item_unlock_stale(bip); - ASSERT(bip->__bli_format.blf_flags & XFS_BLF_CANCEL); - if (!aborted) { - atomic_dec(&bip->bli_refcount); - return; - } - } - trace_xfs_buf_item_unlock(bip); /* - * If the buf item isn't tracking any data, free it, otherwise drop the - * reference we hold to it. If we are aborting the transaction, this may - * be the only reference to the buf item, so we free it anyway - * regardless of whether it is dirty or not. A dirty abort implies a - * shutdown, anyway. - * * The bli dirty state should match whether the blf has logged segments * except for ordered buffers, where only the bli should be dirty. */ ASSERT((!ordered && dirty == xfs_buf_item_dirty_format(bip)) || (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); /* - * Clean buffers, by definition, cannot be in the AIL. However, aborted - * buffers may be in the AIL regardless of dirty state. An aborted - * transaction that invalidates a buffer already in the AIL may have - * marked it stale and cleared the dirty state, for example. - * - * Therefore if we are aborting a buffer and we've just taken the last - * reference away, we have to check if it is in the AIL before freeing - * it. We need to free it in this case, because an aborted transaction - * has already shut the filesystem down and this is the last chance we - * will have to do so. + * Clear the buffer's association with this transaction and + * per-transaction state from the bli, which has been copied above. + */ + bp->b_transp = NULL; + 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. */ - if (atomic_dec_and_test(&bip->bli_refcount)) { - if (aborted) { - ASSERT(XFS_FORCED_SHUTDOWN(lip->li_mountp)); + 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 (!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); + return; } + ASSERT(!stale || (aborted && freed)); if (!hold) xfs_buf_relse(bp); diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h index ad315e83bc02..3043e5ed6495 100644 --- a/fs/xfs/xfs_trace.h +++ b/fs/xfs/xfs_trace.h @@ -473,7 +473,6 @@ DEFINE_BUF_ITEM_EVENT(xfs_buf_item_pin); DEFINE_BUF_ITEM_EVENT(xfs_buf_item_unpin); DEFINE_BUF_ITEM_EVENT(xfs_buf_item_unpin_stale); DEFINE_BUF_ITEM_EVENT(xfs_buf_item_unlock); -DEFINE_BUF_ITEM_EVENT(xfs_buf_item_unlock_stale); DEFINE_BUF_ITEM_EVENT(xfs_buf_item_committed); DEFINE_BUF_ITEM_EVENT(xfs_buf_item_push); DEFINE_BUF_ITEM_EVENT(xfs_trans_get_buf); -- cgit v1.2.3