commit e5d6b12fe14e89ea1c494585c47b1dfb31d71183
Author: Chris Mason [off-list ref]
Date:   Fri Dec 9 05:56:33 2016 -0800

    Btrfs: don't WARN() in btrfs_transaction_abort() for IO errors

    btrfs_transaction_abort() has a WARN() to help us nail down whatever
    problem lead to the abort.  But most of the time, we're aborting for EIO,
    and the warning just adds noise.

    Signed-off-by: Chris Mason [off-list ref]

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index fc1864a..50bcfb8 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h

@@ -3445,9 +3445,14 @@ do {                                                             \
        /* Report first abort since mount */                    \
        if (!test_and_set_bit(BTRFS_FS_STATE_TRANS_ABORTED,     \
                        &((trans)->fs_info->fs_state))) {       \
-               WARN(1, KERN_DEBUG                              \
-               "BTRFS: Transaction aborted (error %d)\n",      \
-               (errno));                                       \
+               if ((errno) != -EIO) {                          \
+                       WARN(1, KERN_DEBUG                              \
+                       "BTRFS: Transaction aborted (error %d)\n",      \
+                       (errno));                                       \
+               } else {                                                \
+                       pr_debug("BTRFS: Transaction aborted (error %d)\n", \
+                                 (errno));                     \
+               }                                               \
        }                                                       \
        __btrfs_abort_transaction((trans), __func__,            \
                                  __LINE__, (errno));           \

Can we use btrfs_debug here instead?  There are a few naked pr_* calls left
but most of them are either continuing prior lines or don't have an fsinfo available.