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Subject[PATCH] (1/11) fs/super.c fixes
	Linus, I'm resending the second series of superblock handling
fixes. There are 11 chunks (the largest being 5Kb) - I'm sending each
of them in a separate mail (with descriptions). This stuff finally
closes the get_super() races and seriously cleans superblock handling.
It had been in -ac for a while (and got more than a month of testing on
local boxen). Please, apply.

Part 1/11

We grab exclusive lock on ->s_umount() in get_sb_...() and release it
once vfsmount is formed (by do_add_mount()). No deadlocks, since all
activity in protected area is already not allowed to lead to anything
that would grab ->s_umount. We hold ->s_lock over the whole non-trivial part
and anything of that kind would deadlock on it.

We are almost done with the get_super() races by now.

diff -urN S9-pre3/fs/super.c S9-pre3-s_umount/fs/super.c
--- S9-pre3/fs/super.c Sat Aug 11 14:59:24 2001
+++ S9-pre3-s_umount/fs/super.c Mon Aug 13 21:21:26 2001
@@ -820,6 +820,7 @@
spin_lock(&sb_lock);
list_add (&s->s_list, super_blocks.prev);
spin_unlock(&sb_lock);
+ down_write(&s->s_umount);
lock_super(s);
if (!type->read_super(s, data, silent))
goto out_fail;
@@ -839,7 +840,7 @@
spin_lock(&sb_lock);
list_del(&s->s_list);
spin_unlock(&sb_lock);
- __put_super(s);
+ put_super(s);
return NULL;
}

@@ -919,7 +920,9 @@
spin_unlock(&sb_lock);
}
atomic_inc(&sb->s_active);
+ /* Next chunk will drop it */
up_read(&sb->s_umount);
+ down_write(&sb->s_umount);
path_release(&nd);
return sb;
}
@@ -986,6 +989,7 @@
BUG();
atomic_inc(&sb->s_active);
do_remount_sb(sb, flags, data);
+ down_write(&sb->s_umount);
return sb;
}

@@ -1104,6 +1108,7 @@
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
type->kern_mnt = mnt;
+ up_write(&sb->s_umount);
return mnt;
}

@@ -1379,6 +1384,7 @@
mnt->mnt_root = dget(sb->s_root);
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
+ up_write(&sb->s_umount);

/* Something was mounted here while we slept */
while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
@@ -1639,6 +1645,7 @@
fs_type = sb->s_type;
atomic_inc(&sb->s_active);
up_read(&sb->s_umount);
+ down_write(&sb->s_umount);
goto mount_it;
}

@@ -1659,6 +1666,8 @@
panic("VFS: Unable to mount root fs on %s", kdevname(ROOT_DEV));

mount_it:
+ /* FIXME */
+ up_write(&sb->s_umount);
printk ("VFS: Mounted root (%s filesystem)%s.\n",
fs_type->name,
(sb->s_flags & MS_RDONLY) ? " readonly" : "");
-
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