[PATCH] r/o bind mounts: drop write during emergency remount

The emergency remount code forcibly removes FMODE_WRITE from
filps.  The r/o bind mount code notices that this was done
without a proper mnt_drop_write() and properly gives a
warning.

This patch does a mnt_drop_write() to keep everything
balanced.

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 19 insertions, 2 deletions

diff --git a/fs/super.c b/fs/super.c
index 09008dbd264e..01d5c40e9119 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -37,6 +37,7 @@
 #include <linux/idr.h>
 #include <linux/kobject.h>
 #include <linux/mutex.h>
+#include <linux/file.h>
 #include <asm/uaccess.h>
 
 
@@ -567,10 +568,26 @@ static void mark_files_ro(struct super_block *sb)
 {
         struct file *f;
 
+retry:
         file_list_lock();
         list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
-                if (S_ISREG(f->f_path.dentry->d_inode->i_mode) && file_count(f))
-                        f->f_mode &= ~FMODE_WRITE;
+                struct vfsmount *mnt;
+                if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
+                       continue;
+                if (!file_count(f))
+                        continue;
+                if (!(f->f_mode & FMODE_WRITE))
+                        continue;
+                f->f_mode &= ~FMODE_WRITE;
+                mnt = mntget(f->f_path.mnt);
+                file_list_unlock();
+                /*
+                 * This can sleep, so we can't hold
+                 * the file_list_lock() spinlock.
+                 */
+                mnt_drop_write(mnt);
+                mntput(mnt);
+                goto retry;
         }
         file_list_unlock();
 }