linux-kernel - [RFC][PATCH 09/30] r/o bind mounts: drop write during emergency remount

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Date:	Fri, 08 Feb 2008 14:26:58 -0800
From:	Dave Hansen <haveblue@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	hch@....de, viro@...IV.linux.org.uk, viro@....linux.org.uk,
	miklos@...redi.hu, Dave Hansen <haveblue@...ibm.com>
Subject: [RFC][PATCH 09/30] 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.
	
Signed-off-by: Dave Hansen <haveblue@...ibm.com>
---

 linux-2.6.git-dave/fs/super.c |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff -puN fs/super.c~robind-sysrq-fix fs/super.c
--- linux-2.6.git/fs/super.c~robind-sysrq-fix	2008-02-08 13:04:48.000000000 -0800
+++ linux-2.6.git-dave/fs/super.c	2008-02-08 13:04:49.000000000 -0800
@@ -37,6 +37,7 @@
 #include <linux/idr.h>
 #include <linux/kobject.h>
 #include <linux/mutex.h>
+#include <linux/file.h>
 #include <asm/uaccess.h>
 
 
@@ -566,10 +567,25 @@ static void mark_files_ro(struct super_b
 {
 	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 = f->f_path.mnt;
+		file_list_unlock();
+		/*
+		 * This can sleep, so we can't hold
+		 * the file_list_lock() spinlock.
+		 */
+		mnt_drop_write(mnt);
+		goto retry;
 	}
 	file_list_unlock();
 }
_
--
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