[PATCH] r/o bind mounts: debugging for missed calls
There have been a few oopses caused by 'struct file's with NULL f_vfsmnts.
There was also a set of potentially missed mnt_want_write()s from
dentry_open() calls.
This patch provides a very simple debugging framework to catch these kinds of
bugs. It will WARN_ON() them, but should stop us from having any oopses or
mnt_writer count imbalances.
I'm quite convinced that this is a good thing because it found bugs in the
stuff I was working on as soon as I wrote it.
[hch: made it conditional on a debug option.
But it's still a little bit too ugly]
[hch: merged forced remount r/o fix from Dave and akpm's fix for the fix]
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/file_table.c b/fs/file_table.c
index 71efc70..7a0a9b8 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -42,6 +42,7 @@
static inline void file_free(struct file *f)
{
percpu_counter_dec(&nr_files);
+ file_check_state(f);
call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
}
@@ -207,6 +208,7 @@
* that we can do debugging checks at __fput()
*/
if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) {
+ file_take_write(file);
error = mnt_want_write(mnt);
WARN_ON(error);
}
@@ -237,8 +239,13 @@
struct inode *inode = dentry->d_inode;
put_write_access(inode);
- if (!special_file(inode->i_mode))
- mnt_drop_write(mnt);
+
+ if (special_file(inode->i_mode))
+ return;
+ if (file_check_writeable(file) != 0)
+ return;
+ mnt_drop_write(mnt);
+ file_release_write(file);
}
EXPORT_SYMBOL_GPL(drop_file_write_access);