fs: assign sb->s_bdi to default_backing_dev_info if the bdi is going away

commit 95f28604a65b1c40b6c6cd95e58439cd7ded3add upstream.

We don't have proper reference counting for this yet, so we run into
cases where the device is pulled and we OOPS on flushing the fs data.
This happens even though the dirty inodes have already been
migrated to the default_backing_dev_info.

Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Tested-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/super.c b/fs/super.c
index ca69615..302356f 100644 (file)
--- a/fs/super.c
+++ b/fs/super.c
@@ -70,6 +70,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
 #else
                INIT_LIST_HEAD(&s->s_files);
 #endif
+               s->s_bdi = &default_backing_dev_info;
                INIT_LIST_HEAD(&s->s_instances);
                INIT_HLIST_HEAD(&s->s_anon);
                INIT_LIST_HEAD(&s->s_inodes);
@@ -996,6 +997,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
        }
        BUG_ON(!mnt->mnt_sb);
        WARN_ON(!mnt->mnt_sb->s_bdi);
+       WARN_ON(mnt->mnt_sb->s_bdi == &default_backing_dev_info);
        mnt->mnt_sb->s_flags |= MS_BORN;
 
        error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);

diff --git a/fs/sync.c b/fs/sync.c
index ba76b96..412dc89 100644 (file)
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -33,7 +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 || sb->s_bdi == &noop_backing_dev_info)
+       if (sb->s_bdi == &noop_backing_dev_info)
                return 0;
 
        if (sb->s_qcop && sb->s_qcop->quota_sync)
@@ -79,7 +79,7 @@ EXPORT_SYMBOL_GPL(sync_filesystem);
 
 static void sync_one_sb(struct super_block *sb, void *arg)
 {
-       if (!(sb->s_flags & MS_RDONLY) && sb->s_bdi)
+       if (!(sb->s_flags & MS_RDONLY))
                __sync_filesystem(sb, *(int *)arg);
 }
 /*

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 027100d..8e4ed88 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -604,7 +604,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
        spin_lock(&sb_lock);
        list_for_each_entry(sb, &super_blocks, s_list) {
                if (sb->s_bdi == bdi)
-                       sb->s_bdi = NULL;
+                       sb->s_bdi = &default_backing_dev_info;
        }
        spin_unlock(&sb_lock);
 }