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SubjectRe: a major regression in recent kernels? - was: Re: Null pointer OOPS in sync_inodes_sb+0xa9/0x104
George,

If you can reproduce this easily, can you try with this patch? When we
move the potential dirty list entries to the default_backing_dev_info,
reassign the sb->s_bdi as well. default_backing_dev_info will always be
around. I hope this can fix it up for 2.6.38 and we can add the proper
ref counting for .39.

diff --git a/fs/super.c b/fs/super.c
index 7e9dd4c..0d89e93 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -71,6 +71,7 @@ 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_BL_HEAD(&s->s_anon);
INIT_LIST_HEAD(&s->s_inodes);
@@ -1003,6 +1004,7 @@ 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
--- 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
--- 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);
}
--
Jens Axboe



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