From 14da9200140f8d722ad1767dfabadebd8b34f2ad Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 12 Jun 2012 16:20:37 +0200 Subject: fs: Protect write paths by sb_start_write - sb_end_write There are several entry points which dirty pages in a filesystem. mmap (handled by block_page_mkwrite()), buffered write (handled by __generic_file_aio_write()), splice write (generic_file_splice_write), truncate, and fallocate (these can dirty last partial page - handled inside each filesystem separately). Protect these places with sb_start_write() and sb_end_write(). ->page_mkwrite() calls are particularly complex since they are called with mmap_sem held and thus we cannot use standard sb_start_write() due to lock ordering constraints. We solve the problem by using a special freeze protection sb_start_pagefault() which ranks below mmap_sem. 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 --- mm/filemap.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index 51efee65c2cc..fa5ca304148e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1718,6 +1718,7 @@ int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) struct inode *inode = vma->vm_file->f_path.dentry->d_inode; int ret = VM_FAULT_LOCKED; + sb_start_pagefault(inode->i_sb); file_update_time(vma->vm_file); lock_page(page); if (page->mapping != inode->i_mapping) { @@ -1725,7 +1726,14 @@ int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) ret = VM_FAULT_NOPAGE; goto out; } + /* + * We mark the page dirty already here so that when freeze is in + * progress, we are guaranteed that writeback during freezing will + * see the dirty page and writeprotect it again. + */ + set_page_dirty(page); out: + sb_end_pagefault(inode->i_sb); return ret; } EXPORT_SYMBOL(filemap_page_mkwrite); @@ -2426,8 +2434,6 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov, count = ocount; pos = *ppos; - vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE); - /* We can write back this queue in page reclaim */ current->backing_dev_info = mapping->backing_dev_info; written = 0; @@ -2526,6 +2532,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov, BUG_ON(iocb->ki_pos != pos); + sb_start_write(inode->i_sb); mutex_lock(&inode->i_mutex); blk_start_plug(&plug); ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos); @@ -2539,6 +2546,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov, ret = err; } blk_finish_plug(&plug); + sb_end_write(inode->i_sb); return ret; } EXPORT_SYMBOL(generic_file_aio_write); -- cgit v1.2.3