Catch filesystems lacking s_bdi

noop_backing_dev_info is used only as a flag to mark filesystems that
don't have any backing store, like tmpfs, procfs, spufs, etc.

Signed-off-by: Joern Engel <joern@logfs.org>

Changed the BUG_ON() to a WARN_ON(). Note that adding dirty inodes
to the noop_backing_dev_info is not legal and will not result in
them being flushed, but we already catch this condition in
__mark_inode_dirty() when checking for a registered bdi.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

4 files changed, 13 insertions, 4 deletions

diff --git a/fs/super.c b/fs/super.c
index f35ac6022109..dc72491a19f9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -693,6 +693,7 @@ int set_anon_super(struct super_block *s, void *data)
                 return -EMFILE;
         }
         s->s_dev = MKDEV(0, dev & MINORMASK);
+        s->s_bdi = &noop_backing_dev_info;
         return 0;
 }
 
@@ -954,10 +955,11 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
         if (error < 0)
                 goto out_free_secdata;
         BUG_ON(!mnt->mnt_sb);
+        WARN_ON(!mnt->mnt_sb->s_bdi);
 
-        error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
-        if (error)
-                goto out_sb;
+        error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
+        if (error)
+                goto out_sb;
 
         /*
          * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
diff --git a/fs/sync.c b/fs/sync.c
index fc5c3d75cf3c..92b228176f7c 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -14,6 +14,7 @@
 #include <linux/pagemap.h>
 #include <linux/quotaops.h>
 #include <linux/buffer_head.h>
+#include <linux/backing-dev.h>
 #include "internal.h"
 
 #define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
@@ -32,7 +33,7 @@ static int __sync_filesystem(struct super_block *sb, int wait)
          * This should be safe, as we require bdi backing to actually
          * write out data in the first place
          */
-        if (!sb->s_bdi)
+        if (!sb->s_bdi || sb->s_bdi == &noop_backing_dev_info)
                 return 0;
 
         if (sb->s_qcop && sb->s_qcop->quota_sync)
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index e19c677f219c..bd0e3c6f323f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -247,6 +247,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 #endif
 
 extern struct backing_dev_info default_backing_dev_info;
+extern struct backing_dev_info noop_backing_dev_info;
 void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page);
 
 int writeback_in_progress(struct backing_dev_info *bdi);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index dbda4707f593..707d0dc6da0f 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -27,6 +27,11 @@ struct backing_dev_info default_backing_dev_info = {
 };
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
 
+struct backing_dev_info noop_backing_dev_info = {
+        .name           = "noop",
+};
+EXPORT_SYMBOL_GPL(noop_backing_dev_info);
+
 static struct class *bdi_class;
 
 /*