[PATCH v3 27/33] gfs2: wait for a pending withdraw before remounting read-only

[Christian Brauner <brauner@kernel.org>]

Since commit 9c4a3de6cd5b ("gfs2: Asynchronous withdraw") most of a
withdraw happens in do_withdraw() from a work item and SDF_JOURNAL_LIVE
stays set until then. A remount to read-only in that window bails out of
its log flushes on the withdrawn filesystem and gfs2_quota_cleanup()
hits its BUG_ON(). Flushing the work isn't enough because
gfs2_withdraw() only queues it after setting SDF_WITHDRAWN and a
withdraw can also start in the middle of gfs2_make_fs_ro().

So let do_withdraw() wake up waiters when it clears SDF_JOURNAL_LIVE and
let gfs2_make_fs_ro() wait for that right before gfs2_quota_cleanup().
umount doesn't need to wait because it sets SDF_NORECOVERY first.

gfs2_make_fs_rw() could leave the bit set on a withdrawn filesystem too
if do_withdraw() ran between its withdraw check and setting the bit. So
do both under sd_log_flush_lock which do_withdraw() holds while it tests
the bit.

Fixes: 9c4a3de6cd5b ("gfs2: Asynchronous withdraw")
Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/gfs2/super.c | 20 ++++++++++++++++----
 fs/gfs2/util.c  |  2 +-
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 04bb4cf787d4d..f61c309368ef1 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -146,12 +146,21 @@ int gfs2_make_fs_rw(struct gfs2_sbd *sdp)
 	}
 
 	error = gfs2_quota_init(sdp);
-	if (!error && gfs2_withdrawn(sdp)) {
-		gfs2_quota_cleanup(sdp);
+	if (error)
+		return error;
+
+	/*
+	 * Check for a withdraw under the lock do_withdraw() holds while it
+	 * takes a live journal down, so one of them sees the other.
+	 */
+	down_write(&sdp->sd_log_flush_lock);
+	if (gfs2_withdrawn(sdp))
 		error = -EIO;
-	}
-	if (!error)
+	else
 		set_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags);
+	up_write(&sdp->sd_log_flush_lock);
+	if (error)
+		gfs2_quota_cleanup(sdp);
 	return error;
 }
 
@@ -567,6 +576,9 @@ void gfs2_make_fs_ro(struct gfs2_sbd *sdp)
 				   HZ * 5);
 		gfs2_assert_warn(sdp, gfs2_log_is_empty(sdp));
 	}
+	/* A withdraw that do_withdraw() didn't finish yet leaves it live. */
+	if (!test_bit(SDF_NORECOVERY, &sdp->sd_flags))
+		wait_on_bit(&sdp->sd_flags, SDF_JOURNAL_LIVE, TASK_UNINTERRUPTIBLE);
 	gfs2_quota_cleanup(sdp);
 }
 
diff --git a/fs/gfs2/util.c b/fs/gfs2/util.c
index 529c3ec37a18a..888e0d6bf5122 100644
--- a/fs/gfs2/util.c
+++ b/fs/gfs2/util.c
@@ -121,7 +121,7 @@ static void do_withdraw(struct gfs2_sbd *sdp)
 		up_write(&sdp->sd_log_flush_lock);
 		return;
 	}
-	clear_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags);
+	clear_and_wake_up_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags);
 	gfs2_ail_drain(sdp); /* frees all transactions */
 	up_write(&sdp->sd_log_flush_lock);
 

-- 
2.53.0