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Message-Id: <1339510848-16992-15-git-send-email-jack@suse.cz>
Date: Tue, 12 Jun 2012 16:20:35 +0200
From: Jan Kara <jack@...e.cz>
To: Al Viro <viro@...IV.linux.org.uk>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...e.cz,
Jan Kara <jack@...e.cz>
Subject: [PATCH 14/27] fs: Add freezing handling to mnt_want_write() / mnt_drop_write()
Most of places where we want freeze protection coincides with the places where
we also have remount-ro protection. So make mnt_want_write() and
mnt_drop_write() (and their _file alternative) prevent freezing as well.
For the few cases that are really interested only in remount-ro protection
provide new function variants.
BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@...onical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@...onical.com>
Tested-by: Dann Frazier <dann.frazier@...onical.com>
Tested-by: Massimo Morana <massimo.morana@...onical.com>
Signed-off-by: Jan Kara <jack@...e.cz>
---
fs/file_table.c | 2 +-
fs/inode.c | 4 +-
fs/namei.c | 15 ++++++-
fs/namespace.c | 101 +++++++++++++++++++++++++++++++++++++++----------
fs/open.c | 2 +-
include/linux/mount.h | 4 ++
6 files changed, 102 insertions(+), 26 deletions(-)
diff --git a/fs/file_table.c b/fs/file_table.c
index a305d9e..5fcaa56 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -215,7 +215,7 @@ static void drop_file_write_access(struct file *file)
return;
if (file_check_writeable(file) != 0)
return;
- mnt_drop_write(mnt);
+ __mnt_drop_write(mnt);
file_release_write(file);
}
diff --git a/fs/inode.c b/fs/inode.c
index c99163b..f23fbd1 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1660,11 +1660,11 @@ int file_update_time(struct file *file)
return 0;
/* Finally allowed to write? Takes lock. */
- if (mnt_want_write_file(file))
+ if (__mnt_want_write_file(file))
return 0;
ret = update_time(inode, &now, sync_it);
- mnt_drop_write_file(file);
+ __mnt_drop_write_file(file);
return ret;
}
diff --git a/fs/namei.c b/fs/namei.c
index 6e65207..81fd4ef 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2270,12 +2270,20 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
goto exit;
retry_lookup:
+ /*
+ * We don't know whether write access will be needed or not. But we
+ * must get the protection before getting i_mutex due to locking
+ * constraints. Thus O_CREAT open will get blocked on frozen filesystem
+ * even if it didn't need to create anything. Not that surprising...
+ */
+ sb_start_write(dir->d_sb);
mutex_lock(&dir->d_inode->i_mutex);
dentry = lookup_hash(nd);
error = PTR_ERR(dentry);
if (IS_ERR(dentry)) {
mutex_unlock(&dir->d_inode->i_mutex);
+ sb_end_write(dir->d_sb);
goto exit;
}
@@ -2294,9 +2302,11 @@ retry_lookup:
* a permanent write count is taken through
* the 'struct file' in nameidata_to_filp().
*/
- error = mnt_want_write(nd->path.mnt);
- if (error)
+ error = __mnt_want_write(nd->path.mnt);
+ if (error) {
+ sb_end_write(dir->d_sb);
goto exit_mutex_unlock;
+ }
want_write = 1;
/* Don't check for write permission, don't truncate */
open_flag &= ~O_TRUNC;
@@ -2318,6 +2328,7 @@ retry_lookup:
* It already exists.
*/
mutex_unlock(&dir->d_inode->i_mutex);
+ sb_end_write(dir->d_sb);
audit_inode(pathname, path->dentry);
error = -EEXIST;
diff --git a/fs/namespace.c b/fs/namespace.c
index 1e4a5fe..2e36aee 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -283,24 +283,22 @@ static int mnt_is_readonly(struct vfsmount *mnt)
}
/*
- * Most r/o checks on a fs are for operations that take
- * discrete amounts of time, like a write() or unlink().
- * We must keep track of when those operations start
- * (for permission checks) and when they end, so that
- * we can determine when writes are able to occur to
- * a filesystem.
+ * Most r/o & frozen checks on a fs are for operations that take discrete
+ * amounts of time, like a write() or unlink(). We must keep track of when
+ * those operations start (for permission checks) and when they end, so that we
+ * can determine when writes are able to occur to a filesystem.
*/
/**
- * mnt_want_write - get write access to a mount
+ * __mnt_want_write - get write access to a mount without freeze protection
* @m: the mount on which to take a write
*
- * This tells the low-level filesystem that a write is
- * about to be performed to it, and makes sure that
- * writes are allowed before returning success. When
- * the write operation is finished, mnt_drop_write()
- * must be called. This is effectively a refcount.
+ * This tells the low-level filesystem that a write is about to be performed to
+ * it, and makes sure that writes are allowed (mnt it read-write) before
+ * returning success. This operation does not protect against filesystem being
+ * frozen. When the write operation is finished, __mnt_drop_write() must be
+ * called. This is effectively a refcount.
*/
-int mnt_want_write(struct vfsmount *m)
+int __mnt_want_write(struct vfsmount *m)
{
struct mount *mnt = real_mount(m);
int ret = 0;
@@ -326,6 +324,28 @@ int mnt_want_write(struct vfsmount *m)
ret = -EROFS;
}
preempt_enable();
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(__mnt_want_write);
+
+/**
+ * mnt_want_write - get write access to a mount
+ * @m: the mount on which to take a write
+ *
+ * This tells the low-level filesystem that a write is about to be performed to
+ * it, and makes sure that writes are allowed (mount is read-write, filesystem
+ * is not frozen) before returning success. When the write operation is
+ * finished, mnt_drop_write() must be called. This is effectively a refcount.
+ */
+int mnt_want_write(struct vfsmount *m)
+{
+ int ret;
+
+ sb_start_write(m->mnt_sb);
+ ret = __mnt_want_write(m);
+ if (ret)
+ sb_end_write(m->mnt_sb);
return ret;
}
EXPORT_SYMBOL_GPL(mnt_want_write);
@@ -355,38 +375,79 @@ int mnt_clone_write(struct vfsmount *mnt)
EXPORT_SYMBOL_GPL(mnt_clone_write);
/**
- * mnt_want_write_file - get write access to a file's mount
+ * __mnt_want_write_file - get write access to a file's mount
* @file: the file who's mount on which to take a write
*
- * This is like mnt_want_write, but it takes a file and can
+ * This is like __mnt_want_write, but it takes a file and can
* do some optimisations if the file is open for write already
*/
-int mnt_want_write_file(struct file *file)
+int __mnt_want_write_file(struct file *file)
{
struct inode *inode = file->f_dentry->d_inode;
+
if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
- return mnt_want_write(file->f_path.mnt);
+ return __mnt_want_write(file->f_path.mnt);
else
return mnt_clone_write(file->f_path.mnt);
}
+EXPORT_SYMBOL_GPL(__mnt_want_write_file);
+
+/**
+ * mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like mnt_want_write, but it takes a file and can
+ * do some optimisations if the file is open for write already
+ */
+int mnt_want_write_file(struct file *file)
+{
+ int ret;
+
+ sb_start_write(file->f_path.mnt->mnt_sb);
+ ret = __mnt_want_write_file(file);
+ if (ret)
+ sb_end_write(file->f_path.mnt->mnt_sb);
+ return ret;
+}
EXPORT_SYMBOL_GPL(mnt_want_write_file);
/**
- * mnt_drop_write - give up write access to a mount
+ * __mnt_drop_write - give up write access to a mount
* @mnt: the mount on which to give up write access
*
* Tells the low-level filesystem that we are done
* performing writes to it. Must be matched with
- * mnt_want_write() call above.
+ * __mnt_want_write() call above.
*/
-void mnt_drop_write(struct vfsmount *mnt)
+void __mnt_drop_write(struct vfsmount *mnt)
{
preempt_disable();
mnt_dec_writers(real_mount(mnt));
preempt_enable();
}
+EXPORT_SYMBOL_GPL(__mnt_drop_write);
+
+/**
+ * mnt_drop_write - give up write access to a mount
+ * @mnt: the mount on which to give up write access
+ *
+ * Tells the low-level filesystem that we are done performing writes to it and
+ * also allows filesystem to be frozen again. Must be matched with
+ * mnt_want_write() call above.
+ */
+void mnt_drop_write(struct vfsmount *mnt)
+{
+ __mnt_drop_write(mnt);
+ sb_end_write(mnt->mnt_sb);
+}
EXPORT_SYMBOL_GPL(mnt_drop_write);
+void __mnt_drop_write_file(struct file *file)
+{
+ __mnt_drop_write(file->f_path.mnt);
+}
+EXPORT_SYMBOL(__mnt_drop_write_file);
+
void mnt_drop_write_file(struct file *file)
{
mnt_drop_write(file->f_path.mnt);
diff --git a/fs/open.c b/fs/open.c
index d6c79a0..5e129f5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -647,7 +647,7 @@ static inline int __get_file_write_access(struct inode *inode,
/*
* Balanced in __fput()
*/
- error = mnt_want_write(mnt);
+ error = __mnt_want_write(mnt);
if (error)
put_write_access(inode);
}
diff --git a/include/linux/mount.h b/include/linux/mount.h
index d7029f4..d6ffc3d 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -55,10 +55,14 @@ struct vfsmount {
struct file; /* forward dec */
+extern int __mnt_want_write(struct vfsmount *mnt);
extern int mnt_want_write(struct vfsmount *mnt);
+extern int __mnt_want_write_file(struct file *file);
extern int mnt_want_write_file(struct file *file);
extern int mnt_clone_write(struct vfsmount *mnt);
+extern void __mnt_drop_write(struct vfsmount *mnt);
extern void mnt_drop_write(struct vfsmount *mnt);
+extern void __mnt_drop_write_file(struct file *file);
extern void mnt_drop_write_file(struct file *file);
extern void mntput(struct vfsmount *mnt);
extern struct vfsmount *mntget(struct vfsmount *mnt);
--
1.7.1
--
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