Btrfs: Add a thread pool just for submit_bio

If a bio submission is after a lock holder waiting for the bio
on the work queue, it is possible to deadlock.  Move the bios
into their own pool.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 181c81d29897..dcea9d706d9b 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -529,9 +529,13 @@ struct btrfs_fs_info {
          * can run with FS locks held, and the writers may be waiting for
          * those locks.  We don't want ordering in the pending list to cause
          * deadlocks, and so the two are serviced separately.
+         *
+         * A third pool does submit_bio to avoid deadlocking with the other
+         * two
          */
         struct btrfs_workers workers;
         struct btrfs_workers endio_workers;
+        struct btrfs_workers submit_workers;
         int thread_pool_size;
 
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