[PATCH v4] bcachefs: fix deadlock in journal_entry_open()

[Jeongjun Park]

In the previous commit b3d82c2f2761, code was added to prevent journal sequence
overflow. Among them, the code added to journal_entry_open() uses the
bch2_fs_fatal_err_on() function to handle errors.

However, __journal_res_get() , which calls journal_entry_open() , calls
journal_entry_open() while holding journal->lock , but bch2_fs_fatal_err_on()
internally tries to acquire journal->lock , which results in a deadlock.

So we need to add a locked helper to handle fatal errors even when the
journal->lock is held.

Fixes: b3d82c2f2761 ("bcachefs: Guard against journal seq overflow")
Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
---
 fs/bcachefs/journal.c | 17 +++++++++++++++--
 fs/bcachefs/journal.h |  1 +
 fs/bcachefs/super.c   | 11 +++++++++++
 fs/bcachefs/super.h   |  1 +
 4 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
index 2cd20114b74b..123b8b119c8c 100644
--- a/fs/bcachefs/journal.c
+++ b/fs/bcachefs/journal.c
@@ -320,6 +320,16 @@ void bch2_journal_halt(struct journal *j)
 	spin_unlock(&j->lock);
 }
 
+void bch2_journal_halt_locked(struct journal *j)
+{
+	lockdep_assert_held(&j->lock);
+
+	__journal_entry_close(j, JOURNAL_ENTRY_ERROR_VAL, true);
+	if (!j->err_seq)
+		j->err_seq = journal_cur_seq(j);
+	journal_wake(j);
+}
+
 static bool journal_entry_want_write(struct journal *j)
 {
 	bool ret = !journal_entry_is_open(j) ||
@@ -382,9 +392,12 @@ static int journal_entry_open(struct journal *j)
 	if (nr_unwritten_journal_entries(j) == ARRAY_SIZE(j->buf))
 		return JOURNAL_ERR_max_in_flight;
 
-	if (bch2_fs_fatal_err_on(journal_cur_seq(j) >= JOURNAL_SEQ_MAX,
-				 c, "cannot start: journal seq overflow"))
+	if (journal_cur_seq(j) >= JOURNAL_SEQ_MAX) {
+		bch_err(c, "cannot start: journal seq overflow");
+		if (bch2_fs_emergency_read_only_locked(c))
+			bch_err(c, "fatal error - emergency read only");
 		return JOURNAL_ERR_insufficient_devices; /* -EROFS */
+	}
 
 	BUG_ON(!j->cur_entry_sectors);
 
diff --git a/fs/bcachefs/journal.h b/fs/bcachefs/journal.h
index cb0df0663946..416fbed447de 100644
--- a/fs/bcachefs/journal.h
+++ b/fs/bcachefs/journal.h
@@ -408,6 +408,7 @@ bool bch2_journal_noflush_seq(struct journal *, u64, u64);
 int bch2_journal_meta(struct journal *);
 
 void bch2_journal_halt(struct journal *);
+void bch2_journal_halt_locked(struct journal *);
 
 static inline int bch2_journal_error(struct journal *j)
 {
diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
index d97ea7bd1171..6d97d412fed9 100644
--- a/fs/bcachefs/super.c
+++ b/fs/bcachefs/super.c
@@ -411,6 +411,17 @@ bool bch2_fs_emergency_read_only(struct bch_fs *c)
 	return ret;
 }
 
+bool bch2_fs_emergency_read_only_locked(struct bch_fs *c)
+{
+	bool ret = !test_and_set_bit(BCH_FS_emergency_ro, &c->flags);
+
+	bch2_journal_halt_locked(&c->journal);
+	bch2_fs_read_only_async(c);
+
+	wake_up(&bch2_read_only_wait);
+	return ret;
+}
+
 static int bch2_fs_read_write_late(struct bch_fs *c)
 {
 	int ret;
diff --git a/fs/bcachefs/super.h b/fs/bcachefs/super.h
index fa6d52216510..04f8287eff5c 100644
--- a/fs/bcachefs/super.h
+++ b/fs/bcachefs/super.h
@@ -29,6 +29,7 @@ int bch2_dev_resize(struct bch_fs *, struct bch_dev *, u64);
 struct bch_dev *bch2_dev_lookup(struct bch_fs *, const char *);
 
 bool bch2_fs_emergency_read_only(struct bch_fs *);
+bool bch2_fs_emergency_read_only_locked(struct bch_fs *);
 void bch2_fs_read_only(struct bch_fs *);
 
 int bch2_fs_read_write(struct bch_fs *);
--