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authorJan Kara <jack@suse.cz>2012-06-12 16:20:37 +0200
committerAl Viro <viro@zeniv.linux.org.uk>2012-07-31 09:45:47 +0400
commit14da9200140f8d722ad1767dfabadebd8b34f2ad (patch)
treeea5d88b091999f7a64af0b9d335d7cad4c79edfb /fs
parent5d37e9e6dec65cd21be68ee92de99686213e916b (diff)
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 <kamal@canonical.com> Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com> Tested-by: Dann Frazier <dann.frazier@canonical.com> Tested-by: Massimo Morana <massimo.morana@canonical.com> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/buffer.c22
-rw-r--r--fs/open.c7
-rw-r--r--fs/splice.c3
3 files changed, 13 insertions, 19 deletions
diff --git a/fs/buffer.c b/fs/buffer.c
index d5ec360e332..9f6d2e41281 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2306,8 +2306,8 @@ EXPORT_SYMBOL(block_commit_write);
* beyond EOF, then the page is guaranteed safe against truncation until we
* unlock the page.
*
- * Direct callers of this function should call vfs_check_frozen() so that page
- * fault does not busyloop until the fs is thawed.
+ * Direct callers of this function should protect against filesystem freezing
+ * using sb_start_write() - sb_end_write() functions.
*/
int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
get_block_t get_block)
@@ -2345,18 +2345,7 @@ int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
if (unlikely(ret < 0))
goto out_unlock;
- /*
- * Freezing in progress? We check after the page is marked dirty and
- * with page lock held so if the test here fails, we are sure freezing
- * code will wait during syncing until the page fault is done - at that
- * point page will be dirty and unlocked so freezing code will write it
- * and writeprotect it again.
- */
set_page_dirty(page);
- if (inode->i_sb->s_frozen != SB_UNFROZEN) {
- ret = -EAGAIN;
- goto out_unlock;
- }
wait_on_page_writeback(page);
return 0;
out_unlock:
@@ -2371,12 +2360,9 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
int ret;
struct super_block *sb = vma->vm_file->f_path.dentry->d_inode->i_sb;
- /*
- * This check is racy but catches the common case. The check in
- * __block_page_mkwrite() is reliable.
- */
- vfs_check_frozen(sb, SB_FREEZE_WRITE);
+ sb_start_pagefault(sb);
ret = __block_page_mkwrite(vma, vmf, get_block);
+ sb_end_pagefault(sb);
return block_page_mkwrite_return(ret);
}
EXPORT_SYMBOL(block_page_mkwrite);
diff --git a/fs/open.c b/fs/open.c
index 9ddc1856550..f3d96e7e7b1 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -164,11 +164,13 @@ static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
if (IS_APPEND(inode))
goto out_putf;
+ sb_start_write(inode->i_sb);
error = locks_verify_truncate(inode, file, length);
if (!error)
error = security_path_truncate(&file->f_path);
if (!error)
error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, file);
+ sb_end_write(inode->i_sb);
out_putf:
fput(file);
out:
@@ -266,7 +268,10 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
if (!file->f_op->fallocate)
return -EOPNOTSUPP;
- return file->f_op->fallocate(file, mode, offset, len);
+ sb_start_write(inode->i_sb);
+ ret = file->f_op->fallocate(file, mode, offset, len);
+ sb_end_write(inode->i_sb);
+ return ret;
}
SYSCALL_DEFINE(fallocate)(int fd, int mode, loff_t offset, loff_t len)
diff --git a/fs/splice.c b/fs/splice.c
index 7bf08fa22ec..41514dd8946 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -996,6 +996,8 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
};
ssize_t ret;
+ sb_start_write(inode->i_sb);
+
pipe_lock(pipe);
splice_from_pipe_begin(&sd);
@@ -1034,6 +1036,7 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
*ppos += ret;
balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
}
+ sb_end_write(inode->i_sb);
return ret;
}