From eb04c28288bb0098d0e75d81ba2a575239de71d8 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 12 Jun 2012 16:20:35 +0200 Subject: 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 Tested-by: Peter M. Petrakis Tested-by: Dann Frazier Tested-by: Massimo Morana Signed-off-by: Jan Kara Signed-off-by: Al Viro --- fs/namespace.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 77 insertions(+), 20 deletions(-) (limited to 'fs/namespace.c') diff --git a/fs/namespace.c b/fs/namespace.c index c53d3381b0d..4d31f73e256 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 +324,27 @@ int mnt_want_write(struct vfsmount *m) ret = -EROFS; } preempt_enable(); + + return ret; +} + +/** + * 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 +374,76 @@ 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); } + +/** + * 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(); } + +/** + * 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); +} + void mnt_drop_write_file(struct file *file) { mnt_drop_write(file->f_path.mnt); -- cgit v1.2.3