[05/24] btrfs: update flush method assertion when reserving space

Commit Message

Filipe Manana March 21, 2023, 11:13 a.m. UTC

From: Filipe Manana <[e-mail]>

When reserving space, at space-info.c:__reserve_bytes(), we assert that
either the current task is not holding a transacion handle, or, if it is,
that the flush method is not BTRFS_RESERVE_FLUSH_ALL. This is because that
flush method can trigger transaction commits, and therefore could lead to
a deadlock.

However there are other 2 flush methods that can trigger transaction
commits:

1) BTRFS_RESERVE_FLUSH_ALL_STEAL
2) BTRFS_RESERVE_FLUSH_EVICT

So update the assertion to check the flush method is also not one those
two methods if the current task is holding a transaction handle.

Signed-off-by: Filipe Manana <[e-mail]>
---
 fs/btrfs/space-info.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

Patch

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 3eecce86f63f..379a0e778dfb 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -1603,7 +1603,18 @@  static int __reserve_bytes(struct btrfs_fs_info *fs_info,
 	bool pending_tickets;
 
 	ASSERT(orig_bytes);
-	ASSERT(!current->journal_info || flush != BTRFS_RESERVE_FLUSH_ALL);
+	/*
+	 * If have a transaction handle (current->journal_info != NULL), then
+	 * the flush method can not be neither BTRFS_RESERVE_FLUSH_ALL* nor
+	 * BTRFS_RESERVE_FLUSH_EVICT, as we could deadlock because those
+	 * flushing methods can trigger transaction commits.
+	 */
+	if (current->journal_info) {
+		/* One assert per line for easier debugging. */
+		ASSERT(flush != BTRFS_RESERVE_FLUSH_ALL);
+		ASSERT(flush != BTRFS_RESERVE_FLUSH_ALL_STEAL);
+		ASSERT(flush != BTRFS_RESERVE_FLUSH_EVICT);
+	}
 
 	if (flush == BTRFS_RESERVE_FLUSH_DATA)
 		async_work = &fs_info->async_data_reclaim_work;