nilfs2: fix potential hang in nilfs_error on errors=remount-ro

nilfs_error() calls nilfs_detach_segment_constructor() if
errors=remount-ro option is specified, and this may lead to a hang due
to recursive locking of, for instance, nilfs->ns_segctor_sem and
others.

In this case, detaching segment constructor is not necessary because
read-only flag is set to the filesystem and further writes are
blocked.

This fixes the potential hang issue by removing the
nilfs_detach_segment_constructor() call from nilfs_error.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

2 files changed, 9 insertions, 5 deletions

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 9280b0f10792..ab439a7ef2d8 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2875,8 +2875,15 @@ int nilfs_attach_segment_constructor(struct nilfs_sb_info *sbi)
         struct the_nilfs *nilfs = sbi->s_nilfs;
         int err;
 
-        /* Each field of nilfs_segctor is cleared through the initialization
-           of super-block info */
+        if (NILFS_SC(sbi)) {
+                /*
+                 * This happens if the filesystem was remounted
+                 * read/write after nilfs_error degenerated it into a
+                 * read-only mount.
+                 */
+                nilfs_detach_segment_constructor(sbi);
+        }
+
         sbi->s_sc_info = nilfs_segctor_new(sbi);
         if (!sbi->s_sc_info)
                 return -ENOMEM;
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 3f88401a375b..f068270f6c75 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -96,9 +96,6 @@ void nilfs_error(struct super_block *sb, const char *function,
         if (!(sb->s_flags & MS_RDONLY)) {
                 struct the_nilfs *nilfs = sbi->s_nilfs;
 
-                if (!nilfs_test_opt(sbi, ERRORS_CONT))
-                        nilfs_detach_segment_constructor(sbi);
-
                 down_write(&nilfs->ns_sem);
                 if (!(nilfs->ns_mount_state & NILFS_ERROR_FS)) {
                         nilfs->ns_mount_state |= NILFS_ERROR_FS;