jbd2: Make state lock a spinlock

Bit-spinlocks are problematic on PREEMPT_RT if functions which might sleep
on RT, e.g. spin_lock(), alloc/free(), are invoked inside the lock held
region because bit spinlocks disable preemption even on RT.

A first attempt was to replace state lock with a spinlock placed in struct
buffer_head and make the locking conditional on PREEMPT_RT and
DEBUG_BIT_SPINLOCKS.

Jan pointed out that there is a 4 byte hole in struct journal_head where a
regular spinlock fits in and he would not object to convert the state lock
to a spinlock unconditionally.

Aside of solving the RT problem, this also gains lockdep coverage for the
journal head state lock (bit-spinlocks are not covered by lockdep as it's
hard to fit a lockdep map into a single bit).

The trivial change would have been to convert the jbd_*lock_bh_state()
inlines, but that comes with the downside that these functions take a
buffer head pointer which needs to be converted to a journal head pointer
which adds another level of indirection.

As almost all functions which use this lock have a journal head pointer
readily available, it makes more sense to remove the lock helper inlines
and write out spin_*lock() at all call sites.

Fixup all locking comments as well.

Suggested-by: Jan Kara <jack@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Jan Kara <jack@suse.com>
Cc: linux-ext4@vger.kernel.org
Link: https://lore.kernel.org/r/20190809124233.13277-7-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

3 files changed, 57 insertions, 61 deletions

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index a0a191f3df77..8e1ff875de43 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -482,10 +482,10 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 		if (jh->b_committed_data) {
 			struct buffer_head *bh = jh2bh(jh);
 
-			jbd_lock_bh_state(bh);
+			spin_lock(&jh->b_state_lock);
 			jbd2_free(jh->b_committed_data, bh->b_size);
 			jh->b_committed_data = NULL;
-			jbd_unlock_bh_state(bh);
+			spin_unlock(&jh->b_state_lock);
 		}
 		jbd2_journal_refile_buffer(journal, jh);
 	}
@@ -928,7 +928,7 @@ restart_loop:
 		 * done with it.
 		 */
 		get_bh(bh);
-		jbd_lock_bh_state(bh);
+		spin_lock(&jh->b_state_lock);
 		J_ASSERT_JH(jh,	jh->b_transaction == commit_transaction);
 
 		/*
@@ -1024,7 +1024,7 @@ restart_loop:
 		}
 		JBUFFER_TRACE(jh, "refile or unfile buffer");
 		drop_ref = __jbd2_journal_refile_buffer(jh);
-		jbd_unlock_bh_state(bh);
+		spin_unlock(&jh->b_state_lock);
 		if (drop_ref)
 			jbd2_journal_put_journal_head(jh);
 		if (try_to_free)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 1c58859aa592..5d4192f05879 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -363,7 +363,7 @@ int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
 	/* keep subsequent assertions sane */
 	atomic_set(&new_bh->b_count, 1);
 
-	jbd_lock_bh_state(bh_in);
+	spin_lock(&jh_in->b_state_lock);
 repeat:
 	/*
 	 * If a new transaction has already done a buffer copy-out, then
@@ -405,13 +405,13 @@ repeat:
 	if (need_copy_out && !done_copy_out) {
 		char *tmp;
 
-		jbd_unlock_bh_state(bh_in);
+		spin_unlock(&jh_in->b_state_lock);
 		tmp = jbd2_alloc(bh_in->b_size, GFP_NOFS);
 		if (!tmp) {
 			brelse(new_bh);
 			return -ENOMEM;
 		}
-		jbd_lock_bh_state(bh_in);
+		spin_lock(&jh_in->b_state_lock);
 		if (jh_in->b_frozen_data) {
 			jbd2_free(tmp, bh_in->b_size);
 			goto repeat;
@@ -464,7 +464,7 @@ repeat:
 	__jbd2_journal_file_buffer(jh_in, transaction, BJ_Shadow);
 	spin_unlock(&journal->j_list_lock);
 	set_buffer_shadow(bh_in);
-	jbd_unlock_bh_state(bh_in);
+	spin_unlock(&jh_in->b_state_lock);
 
 	return do_escape | (done_copy_out << 1);
 }
@@ -2410,6 +2410,8 @@ static struct journal_head *journal_alloc_journal_head(void)
 		ret = kmem_cache_zalloc(jbd2_journal_head_cache,
 				GFP_NOFS | __GFP_NOFAIL);
 	}
+	if (ret)
+		spin_lock_init(&ret->b_state_lock);
 	return ret;
 }
 
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index f2af4afc690a..7c11afe60532 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -879,7 +879,7 @@ repeat:
 
  	start_lock = jiffies;
 	lock_buffer(bh);
-	jbd_lock_bh_state(bh);
+	spin_lock(&jh->b_state_lock);
 
 	/* If it takes too long to lock the buffer, trace it */
 	time_lock = jbd2_time_diff(start_lock, jiffies);
@@ -929,7 +929,7 @@ repeat:
 
 	error = -EROFS;
 	if (is_handle_aborted(handle)) {
-		jbd_unlock_bh_state(bh);
+		spin_unlock(&jh->b_state_lock);
 		goto out;
 	}
 	error = 0;
@@ -993,7 +993,7 @@ repeat:
 	 */
 	if (buffer_shadow(bh)) {
 		JBUFFER_TRACE(jh, "on shadow: sleep");
-		jbd_unlock_bh_state(bh);
+		spin_unlock(&jh->b_state_lock);
 		wait_on_bit_io(&bh->b_state, BH_Shadow, TASK_UNINTERRUPTIBLE);
 		goto repeat;
 	}
@@ -1014,7 +1014,7 @@ repeat:
 		JBUFFER_TRACE(jh, "generate frozen data");
 		if (!frozen_buffer) {
 			JBUFFER_TRACE(jh, "allocate memory for buffer");
-			jbd_unlock_bh_state(bh);
+			spin_unlock(&jh->b_state_lock);
 			frozen_buffer = jbd2_alloc(jh2bh(jh)->b_size,
 						   GFP_NOFS | __GFP_NOFAIL);
 			goto repeat;
@@ -1033,7 +1033,7 @@ attach_next:
 	jh->b_next_transaction = transaction;
 
 done:
-	jbd_unlock_bh_state(bh);
+	spin_unlock(&jh->b_state_lock);
 
 	/*
 	 * If we are about to journal a buffer, then any revoke pending on it is
@@ -1172,7 +1172,7 @@ int jbd2_journal_get_create_access(handle_t *handle, struct buffer_head *bh)
 	 * that case: the transaction must have deleted the buffer for it to be
 	 * reused here.
 	 */
-	jbd_lock_bh_state(bh);
+	spin_lock(&jh->b_state_lock);
 	J_ASSERT_JH(jh, (jh->b_transaction == transaction ||
 		jh->b_transaction == NULL ||
 		(jh->b_transaction == journal->j_committing_transaction &&
@@ -1207,7 +1207,7 @@ int jbd2_journal_get_create_access(handle_t *handle, struct buffer_head *bh)
 		jh->b_next_transaction = transaction;
 		spin_unlock(&journal->j_list_lock);
 	}
-	jbd_unlock_bh_state(bh);
+	spin_unlock(&jh->b_state_lock);
 
 	/*
 	 * akpm: I added this.  ext3_alloc_branch can pick up new indirect
@@ -1275,13 +1275,13 @@ repeat:
 		committed_data = jbd2_alloc(jh2bh(jh)->b_size,
 					    GFP_NOFS|__GFP_NOFAIL);
 
-	jbd_lock_bh_state(bh);
+	spin_lock(&jh->b_state_lock);
 	if (!jh->b_committed_data) {
 		/* Copy out the current buffer contents into the
 		 * preserved, committed copy. */
 		JBUFFER_TRACE(jh, "generate b_committed data");
 		if (!committed_data) {
-			jbd_unlock_bh_state(bh);
+			spin_unlock(&jh->b_state_lock);
 			goto repeat;
 		}
 
@@ -1289,7 +1289,7 @@ repeat:
 		committed_data = NULL;
 		memcpy(jh->b_committed_data, bh->b_data, bh->b_size);
 	}
-	jbd_unlock_bh_state(bh);
+	spin_unlock(&jh->b_state_lock);
 out:
 	jbd2_journal_put_journal_head(jh);
 	if (unlikely(committed_data))
@@ -1390,16 +1390,16 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 	 */
 	if (jh->b_transaction != transaction &&
 	    jh->b_next_transaction != transaction) {
-		jbd_lock_bh_state(bh);
+		spin_lock(&jh->b_state_lock);
 		J_ASSERT_JH(jh, jh->b_transaction == transaction ||
 				jh->b_next_transaction == transaction);
-		jbd_unlock_bh_state(bh);
+		spin_unlock(&jh->b_state_lock);
 	}
 	if (jh->b_modified == 1) {
 		/* If it's in our transaction it must be in BJ_Metadata list. */
 		if (jh->b_transaction == transaction &&
 		    jh->b_jlist != BJ_Metadata) {
-			jbd_lock_bh_state(bh);
+			spin_lock(&jh->b_state_lock);
 			if (jh->b_transaction == transaction &&
 			    jh->b_jlist != BJ_Metadata)
 				pr_err("JBD2: assertion failure: h_type=%u "
@@ -1409,13 +1409,13 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 				       jh->b_jlist);
 			J_ASSERT_JH(jh, jh->b_transaction != transaction ||
 					jh->b_jlist == BJ_Metadata);
-			jbd_unlock_bh_state(bh);
+			spin_unlock(&jh->b_state_lock);
 		}
 		goto out;
 	}
 
 	journal = transaction->t_journal;
-	jbd_lock_bh_state(bh);
+	spin_lock(&jh->b_state_lock);
 
 	if (jh->b_modified == 0) {
 		/*
@@ -1501,7 +1501,7 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 	__jbd2_journal_file_buffer(jh, transaction, BJ_Metadata);
 	spin_unlock(&journal->j_list_lock);
 out_unlock_bh:
-	jbd_unlock_bh_state(bh);
+	spin_unlock(&jh->b_state_lock);
 out:
 	JBUFFER_TRACE(jh, "exit");
 	return ret;
@@ -1539,11 +1539,13 @@ int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
 
 	BUFFER_TRACE(bh, "entry");
 
-	jbd_lock_bh_state(bh);
+	jh = jbd2_journal_grab_journal_head(bh);
+	if (!jh) {
+		__bforget(bh);
+		return 0;
+	}
 
-	if (!buffer_jbd(bh))
-		goto not_jbd;
-	jh = bh2jh(bh);
+	spin_lock(&jh->b_state_lock);
 
 	/* Critical error: attempting to delete a bitmap buffer, maybe?
 	 * Don't do any jbd operations, and return an error. */
@@ -1664,18 +1666,14 @@ int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
 		spin_unlock(&journal->j_list_lock);
 	}
 drop:
-	jbd_unlock_bh_state(bh);
 	__brelse(bh);
+	spin_unlock(&jh->b_state_lock);
+	jbd2_journal_put_journal_head(jh);
 	if (drop_reserve) {
 		/* no need to reserve log space for this block -bzzz */
 		handle->h_buffer_credits++;
 	}
 	return err;
-
-not_jbd:
-	jbd_unlock_bh_state(bh);
-	__bforget(bh);
-	goto drop;
 }
 
 /**
@@ -1874,7 +1872,7 @@ free_and_exit:
  *
  * j_list_lock is held.
  *
- * jbd_lock_bh_state(jh2bh(jh)) is held.
+ * jh->b_state_lock is held.
  */
 
 static inline void
@@ -1898,7 +1896,7 @@ __blist_add_buffer(struct journal_head **list, struct journal_head *jh)
  *
  * Called with j_list_lock held, and the journal may not be locked.
  *
- * jbd_lock_bh_state(jh2bh(jh)) is held.
+ * jh->b_state_lock is held.
  */
 
 static inline void
@@ -1930,7 +1928,7 @@ static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh)
 	transaction_t *transaction;
 	struct buffer_head *bh = jh2bh(jh);
 
-	J_ASSERT_JH(jh, jbd_is_locked_bh_state(bh));
+	lockdep_assert_held(&jh->b_state_lock);
 	transaction = jh->b_transaction;
 	if (transaction)
 		assert_spin_locked(&transaction->t_journal->j_list_lock);
@@ -1984,11 +1982,11 @@ void jbd2_journal_unfile_buffer(journal_t *journal, struct journal_head *jh)
 
 	/* Get reference so that buffer cannot be freed before we unlock it */
 	get_bh(bh);
-	jbd_lock_bh_state(bh);
+	spin_lock(&jh->b_state_lock);
 	spin_lock(&journal->j_list_lock);
 	__jbd2_journal_unfile_buffer(jh);
 	spin_unlock(&journal->j_list_lock);
-	jbd_unlock_bh_state(bh);
+	spin_unlock(&jh->b_state_lock);
 	jbd2_journal_put_journal_head(jh);
 	__brelse(bh);
 }
@@ -1996,7 +1994,7 @@ void jbd2_journal_unfile_buffer(journal_t *journal, struct journal_head *jh)
 /*
  * Called from jbd2_journal_try_to_free_buffers().
  *
- * Called under jbd_lock_bh_state(bh)
+ * Called under jh->b_state_lock
  */
 static void
 __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
@@ -2083,10 +2081,10 @@ int jbd2_journal_try_to_free_buffers(journal_t *journal,
 		if (!jh)
 			continue;
 
-		jbd_lock_bh_state(bh);
+		spin_lock(&jh->b_state_lock);
 		__journal_try_to_free_buffer(journal, bh);
+		spin_unlock(&jh->b_state_lock);
 		jbd2_journal_put_journal_head(jh);
-		jbd_unlock_bh_state(bh);
 		if (buffer_jbd(bh))
 			goto busy;
 	} while ((bh = bh->b_this_page) != head);
@@ -2107,7 +2105,7 @@ busy:
  *
  * Called under j_list_lock.
  *
- * Called under jbd_lock_bh_state(bh).
+ * Called under jh->b_state_lock.
  */
 static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
 {
@@ -2201,7 +2199,7 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh,
 
 	/* OK, we have data buffer in journaled mode */
 	write_lock(&journal->j_state_lock);
-	jbd_lock_bh_state(bh);
+	spin_lock(&jh->b_state_lock);
 	spin_lock(&journal->j_list_lock);
 
 	/*
@@ -2282,10 +2280,10 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh,
 		 * for commit and try again.
 		 */
 		if (partial_page) {
-			jbd2_journal_put_journal_head(jh);
 			spin_unlock(&journal->j_list_lock);
-			jbd_unlock_bh_state(bh);
+			spin_unlock(&jh->b_state_lock);
 			write_unlock(&journal->j_state_lock);
+			jbd2_journal_put_journal_head(jh);
 			return -EBUSY;
 		}
 		/*
@@ -2297,10 +2295,10 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh,
 		set_buffer_freed(bh);
 		if (journal->j_running_transaction && buffer_jbddirty(bh))
 			jh->b_next_transaction = journal->j_running_transaction;
-		jbd2_journal_put_journal_head(jh);
 		spin_unlock(&journal->j_list_lock);
-		jbd_unlock_bh_state(bh);
+		spin_unlock(&jh->b_state_lock);
 		write_unlock(&journal->j_state_lock);
+		jbd2_journal_put_journal_head(jh);
 		return 0;
 	} else {
 		/* Good, the buffer belongs to the running transaction.
@@ -2324,10 +2322,10 @@ zap_buffer:
 	 * here.
 	 */
 	jh->b_modified = 0;
-	jbd2_journal_put_journal_head(jh);
 	spin_unlock(&journal->j_list_lock);
-	jbd_unlock_bh_state(bh);
+	spin_unlock(&jh->b_state_lock);
 	write_unlock(&journal->j_state_lock);
+	jbd2_journal_put_journal_head(jh);
 zap_buffer_unlocked:
 	clear_buffer_dirty(bh);
 	J_ASSERT_BH(bh, !buffer_jbddirty(bh));
@@ -2414,7 +2412,7 @@ void __jbd2_journal_file_buffer(struct journal_head *jh,
 	int was_dirty = 0;
 	struct buffer_head *bh = jh2bh(jh);
 
-	J_ASSERT_JH(jh, jbd_is_locked_bh_state(bh));
+	lockdep_assert_held(&jh->b_state_lock);
 	assert_spin_locked(&transaction->t_journal->j_list_lock);
 
 	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
@@ -2476,11 +2474,11 @@ void __jbd2_journal_file_buffer(struct journal_head *jh,
 void jbd2_journal_file_buffer(struct journal_head *jh,
 				transaction_t *transaction, int jlist)
 {
-	jbd_lock_bh_state(jh2bh(jh));
+	spin_lock(&jh->b_state_lock);
 	spin_lock(&transaction->t_journal->j_list_lock);
 	__jbd2_journal_file_buffer(jh, transaction, jlist);
 	spin_unlock(&transaction->t_journal->j_list_lock);
-	jbd_unlock_bh_state(jh2bh(jh));
+	spin_unlock(&jh->b_state_lock);
 }
 
 /*
@@ -2490,7 +2488,7 @@ void jbd2_journal_file_buffer(struct journal_head *jh,
  * buffer on that transaction's metadata list.
  *
  * Called under j_list_lock
- * Called under jbd_lock_bh_state(jh2bh(jh))
+ * Called under jh->b_state_lock
  *
  * When this function returns true, there's no next transaction to refile to
  * and the caller has to drop jh reference through
@@ -2501,7 +2499,7 @@ bool __jbd2_journal_refile_buffer(struct journal_head *jh)
 	int was_dirty, jlist;
 	struct buffer_head *bh = jh2bh(jh);
 
-	J_ASSERT_JH(jh, jbd_is_locked_bh_state(bh));
+	lockdep_assert_held(&jh->b_state_lock);
 	if (jh->b_transaction)
 		assert_spin_locked(&jh->b_transaction->t_journal->j_list_lock);
 
@@ -2547,17 +2545,13 @@ bool __jbd2_journal_refile_buffer(struct journal_head *jh)
  */
 void jbd2_journal_refile_buffer(journal_t *journal, struct journal_head *jh)
 {
-	struct buffer_head *bh = jh2bh(jh);
 	bool drop;
 
-	/* Get reference so that buffer cannot be freed before we unlock it */
-	get_bh(bh);
-	jbd_lock_bh_state(bh);
+	spin_lock(&jh->b_state_lock);
 	spin_lock(&journal->j_list_lock);
 	drop = __jbd2_journal_refile_buffer(jh);
-	jbd_unlock_bh_state(bh);
+	spin_unlock(&jh->b_state_lock);
 	spin_unlock(&journal->j_list_lock);
-	__brelse(bh);
 	if (drop)
 		jbd2_journal_put_journal_head(jh);
 }