ext4: fix deadlock in journal_unmap_buffer()

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.  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@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

3 files changed, 86 insertions, 25 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 12d3fbcff59f..cbfe13bf5b2a 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2894,8 +2894,8 @@ 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);
 
@@ -2907,7 +2907,14 @@ 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)
@@ -4314,6 +4321,47 @@ 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.
@@ -4426,16 +4474,28 @@ 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 cd4485db42b3..ddc51a7f4508 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1840,7 +1840,6 @@ 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
@@ -1935,14 +1934,11 @@ 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
@@ -2003,21 +1999,23 @@ 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
@@ -2031,9 +2029,11 @@ 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;
@@ -2044,6 +2044,7 @@ 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 1be23d9fdacb..e30b66346942 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1098,7 +1098,7 @@ void		 jbd2_journal_set_triggers(struct buffer_head *,
 extern int       jbd2_journal_dirty_metadata (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 *);