scoutfs: warn if lock with trans held

We can't block on a lock while holding the transaction open because
that'd stop lock downconversion from syncing to write out items while it
is converting from EX.  Add a warning if we try to acquire a blocking
lock while holding a transaction.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/lock.c

@@ -26,6 +26,7 @@
 #include "cmp.h"
 #include "dlmglue.h"
 #include "inode.h"
+#include "trans.h"
 
 #define LN_FMT "%u.%u.%u.%llu.%llu"
 #define LN_ARG(name) \
@@ -383,6 +384,10 @@ static int lock_name_keys(struct super_block *sb, int mode, int flags,
 	int lkm_flags;
 	int ret;
 
+	if (WARN_ON_ONCE(!(flags & SCOUTFS_LKF_TRYLOCK) &&
+			 scoutfs_trans_held()))
+		return -EINVAL;
+
 	lock = find_alloc_scoutfs_lock(sb, lock_name, type, start, end);
 	if (!lock)
 		return -ENOMEM;

kmod/src/trans.c

@@ -370,6 +370,18 @@ int scoutfs_hold_trans(struct super_block *sb, struct scoutfs_item_count *cnt)
 	return ret;
 }
 
+/*
+ * Return true if the current task has a transaction held.  That is,
+ * true if the current transaction can't finish and be written out if
+ * the current task blocks.
+ */
+bool scoutfs_trans_held(void)
+{
+	struct scoutfs_reservation *rsv = current->journal_info;
+
+	return rsv && rsv->magic == SCOUTFS_RESERVATION_MAGIC;
+}
+
 void scoutfs_trans_track_item(struct super_block *sb, signed items,
 			      signed keys, signed vals)
 {

kmod/src/trans.h

@@ -10,6 +10,7 @@ int scoutfs_file_fsync(struct file *file, loff_t start, loff_t end,
 void scoutfs_trans_restart_sync_deadline(struct super_block *sb);
 
 int scoutfs_hold_trans(struct super_block *sb, struct scoutfs_item_count *cnt);
+bool scoutfs_trans_held(void);
 void scoutfs_release_trans(struct super_block *sb);
 void scoutfs_trans_wake_holders(struct super_block *sb);
 void scoutfs_trans_track_item(struct super_block *sb, signed items,