[Ocfs2-devel] [PATCH 2/2] ext4: Fix deadlock in journal_unmap_buffer()
Theodore Ts'o
tytso at mit.edu
Fri Dec 21 11:52:20 PST 2012
On Wed, Dec 12, 2012 at 09:50:16PM +0100, Jan Kara wrote:
> We cannot wait for transaction commit in journal_unmap_buffer() because we hold
> page lock which ranks below transaction start. We solve the issue by bailing
> out of journal_unmap_buffer() and jbd2_journal_invalidatepage() with -EBUSY.
ocfs2 also calls jbd2_journal_invalidatepage(). I would think we
would need to apply a similar fix up to ocfs2, lest they end up having
jbd2_journal_invalidatepage() silently failing for them.
I'm going to hold off on this patch until we're sure it's not going to
cause problems for ocfs2. A quick check indicates that they also
support sub-page block sizes, which would tend to indicate that they
could get hit by the same dead lock, yes?
- Ted
> Caller is then responsible for waiting for transaction commit to finish and try
> invalidation again. Since the issue can happen only for page stradding i_size,
> it is simple enough to manually call jbd2_journal_invalidatepage() for such
> page from ext4_setattr(), check the return value and wait if necessary.
>
> Signed-off-by: Jan Kara <jack at suse.cz>
> ---
> fs/ext4/inode.c | 82 +++++++++++++++++++++++++++++++++++++------
> fs/jbd2/transaction.c | 27 +++++++-------
> include/linux/jbd2.h | 2 +-
> include/trace/events/ext4.h | 4 +-
> 4 files changed, 88 insertions(+), 27 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 66abac7..cc0abeb 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2813,8 +2813,8 @@ static void ext4_invalidatepage(struct page *page, unsigned long offset)
> block_invalidatepage(page, offset);
> }
>
> -static void ext4_journalled_invalidatepage(struct page *page,
> - unsigned long offset)
> +static int __ext4_journalled_invalidatepage(struct page *page,
> + unsigned long offset)
> {
> journal_t *journal = EXT4_JOURNAL(page->mapping->host);
>
> @@ -2826,7 +2826,14 @@ static void ext4_journalled_invalidatepage(struct page *page,
> if (offset == 0)
> ClearPageChecked(page);
>
> - jbd2_journal_invalidatepage(journal, page, offset);
> + return jbd2_journal_invalidatepage(journal, page, offset);
> +}
> +
> +/* Wrapper for aops... */
> +static void ext4_journalled_invalidatepage(struct page *page,
> + unsigned long offset)
> +{
> + WARN_ON(__ext4_journalled_invalidatepage(page, offset) < 0);
> }
>
> static int ext4_releasepage(struct page *page, gfp_t wait)
> @@ -4230,6 +4237,47 @@ int ext4_write_inode(struct inode *inode, struct writeback_control *wbc)
> }
>
> /*
> + * In data=journal mode ext4_journalled_invalidatepage() may fail to invalidate
> + * buffers that are attached to a page stradding i_size and are undergoing
> + * commit. In that case we have to wait for commit to finish and try again.
> + */
> +static void ext4_wait_for_tail_page_commit(struct inode *inode)
> +{
> + struct page *page;
> + unsigned offset;
> + journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> + tid_t commit_tid = 0;
> + int ret;
> +
> + offset = inode->i_size & (PAGE_CACHE_SIZE - 1);
> + /*
> + * All buffers in the last page remain valid? Then there's nothing to
> + * do. We do the check mainly to optimize the common PAGE_CACHE_SIZE ==
> + * blocksize case
> + */
> + if (offset > PAGE_CACHE_SIZE - (1 << inode->i_blkbits))
> + return;
> + while (1) {
> + page = find_lock_page(inode->i_mapping,
> + inode->i_size >> PAGE_CACHE_SHIFT);
> + if (!page)
> + return;
> + ret = __ext4_journalled_invalidatepage(page, offset);
> + unlock_page(page);
> + page_cache_release(page);
> + if (ret != -EBUSY)
> + return;
> + commit_tid = 0;
> + read_lock(&journal->j_state_lock);
> + if (journal->j_committing_transaction)
> + commit_tid = journal->j_committing_transaction->t_tid;
> + read_unlock(&journal->j_state_lock);
> + if (commit_tid)
> + jbd2_log_wait_commit(journal, commit_tid);
> + }
> +}
> +
> +/*
> * ext4_setattr()
> *
> * Called from notify_change.
> @@ -4342,16 +4390,28 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
> }
>
> if (attr->ia_valid & ATTR_SIZE) {
> - if (attr->ia_size != i_size_read(inode)) {
> - truncate_setsize(inode, attr->ia_size);
> - /* Inode size will be reduced, wait for dio in flight.
> - * Temporarily disable dioread_nolock to prevent
> - * livelock. */
> + if (attr->ia_size != inode->i_size) {
> + loff_t oldsize = inode->i_size;
> +
> + i_size_write(inode, attr->ia_size);
> + /*
> + * Blocks are going to be removed from the inode. Wait
> + * for dio in flight. Temporarily disable
> + * dioread_nolock to prevent livelock.
> + */
> if (orphan) {
> - ext4_inode_block_unlocked_dio(inode);
> - inode_dio_wait(inode);
> - ext4_inode_resume_unlocked_dio(inode);
> + if (!ext4_should_journal_data(inode)) {
> + ext4_inode_block_unlocked_dio(inode);
> + inode_dio_wait(inode);
> + ext4_inode_resume_unlocked_dio(inode);
> + } else
> + ext4_wait_for_tail_page_commit(inode);
> }
> + /*
> + * Truncate pagecache after we've waited for commit
> + * in data=journal mode to make pages freeable.
> + */
> + truncate_pagecache(inode, oldsize, inode->i_size);
> }
> ext4_truncate(inode);
> }
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index a74ba46..e1475b4 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -1850,7 +1850,6 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh,
>
> BUFFER_TRACE(bh, "entry");
>
> -retry:
> /*
> * It is safe to proceed here without the j_list_lock because the
> * buffers cannot be stolen by try_to_free_buffers as long as we are
> @@ -1945,14 +1944,11 @@ retry:
> * for commit and try again.
> */
> if (partial_page) {
> - tid_t tid = journal->j_committing_transaction->t_tid;
> -
> jbd2_journal_put_journal_head(jh);
> spin_unlock(&journal->j_list_lock);
> jbd_unlock_bh_state(bh);
> write_unlock(&journal->j_state_lock);
> - jbd2_log_wait_commit(journal, tid);
> - goto retry;
> + return -EBUSY;
> }
> /*
> * OK, buffer won't be reachable after truncate. We just set
> @@ -2013,21 +2009,23 @@ zap_buffer_unlocked:
> * @page: page to flush
> * @offset: length of page to invalidate.
> *
> - * Reap page buffers containing data after offset in page.
> - *
> + * Reap page buffers containing data after offset in page. Can return -EBUSY
> + * if buffers are part of the committing transaction and the page is straddling
> + * i_size. Caller then has to wait for current commit and try again.
> */
> -void jbd2_journal_invalidatepage(journal_t *journal,
> - struct page *page,
> - unsigned long offset)
> +int jbd2_journal_invalidatepage(journal_t *journal,
> + struct page *page,
> + unsigned long offset)
> {
> struct buffer_head *head, *bh, *next;
> unsigned int curr_off = 0;
> int may_free = 1;
> + int ret = 0;
>
> if (!PageLocked(page))
> BUG();
> if (!page_has_buffers(page))
> - return;
> + return 0;
>
> /* We will potentially be playing with lists other than just the
> * data lists (especially for journaled data mode), so be
> @@ -2041,9 +2039,11 @@ void jbd2_journal_invalidatepage(journal_t *journal,
> if (offset <= curr_off) {
> /* This block is wholly outside the truncation point */
> lock_buffer(bh);
> - may_free &= journal_unmap_buffer(journal, bh,
> - offset > 0);
> + ret = journal_unmap_buffer(journal, bh, offset > 0);
> unlock_buffer(bh);
> + if (ret < 0)
> + return ret;
> + may_free &= ret;
> }
> curr_off = next_off;
> bh = next;
> @@ -2054,6 +2054,7 @@ void jbd2_journal_invalidatepage(journal_t *journal,
> if (may_free && try_to_free_buffers(page))
> J_ASSERT(!page_has_buffers(page));
> }
> + return 0;
> }
>
> /*
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 3efc43f..cb7d6af 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1099,7 +1099,7 @@ extern int jbd2_journal_dirty_metadata (handle_t *, struct buffer_head *);
> extern void jbd2_journal_release_buffer (handle_t *, struct buffer_head *);
> extern int jbd2_journal_forget (handle_t *, struct buffer_head *);
> extern void journal_sync_buffer (struct buffer_head *);
> -extern void jbd2_journal_invalidatepage(journal_t *,
> +extern int jbd2_journal_invalidatepage(journal_t *,
> struct page *, unsigned long);
> extern int jbd2_journal_try_to_free_buffers(journal_t *, struct page *, gfp_t);
> extern int jbd2_journal_stop(handle_t *);
> diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
> index df972d9..3ef522e 100644
> --- a/include/trace/events/ext4.h
> +++ b/include/trace/events/ext4.h
> @@ -476,13 +476,13 @@ DECLARE_EVENT_CLASS(ext4_invalidatepage_op,
> (unsigned long) __entry->index, __entry->offset)
> );
>
> -DEFINE_EVENT(ext4_invalidatepage_op, ext4_invalidatepage
> +DEFINE_EVENT(ext4_invalidatepage_op, ext4_invalidatepage,
> TP_PROTO(struct page *page, unsigned long offset),
>
> TP_ARGS(page, offset)
> );
>
> -DEFINE_EVENT(ext4_invalidatepage_op, ext4_journalled_invalidatepage
> +DEFINE_EVENT(ext4_invalidatepage_op, ext4_journalled_invalidatepage,
> TP_PROTO(struct page *page, unsigned long offset),
>
> TP_ARGS(page, offset)
> --
> 1.7.1
>
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