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Date: Mon, 5 Mar 2012 17:01:07 +0100
From: Jan Kara <jack@...e.cz>
To: LKML <linux-kernel@...r.kernel.org>
Cc: linux-fsdevel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
Christoph Hellwig <hch@...radead.org>, dchinner@...hat.com,
sandeen@...hat.com, Kamal Mostafa <kamal@...onical.com>,
Jan Kara <jack@...e.cz>
Subject: [PATCH 09/19] 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.
Signed-off-by: Jan Kara <jack@...e.cz>
---
fs/buffer.c | 22 ++++------------------
fs/open.c | 7 ++++++-
fs/splice.c | 3 +++
mm/filemap.c | 12 ++++++++++--
mm/filemap_xip.c | 5 +++--
5 files changed, 26 insertions(+), 23 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 5294a33..89ed4af 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2288,8 +2288,8 @@ 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)
@@ -2327,18 +2327,7 @@ 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:
@@ -2353,12 +2342,9 @@ 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 456e415..444ffbb 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 1ec0493..401297d 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -992,6 +992,8 @@ 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);
@@ -1028,6 +1030,7 @@ 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;
}
diff --git a/mm/filemap.c b/mm/filemap.c
index b865c0b..8ff3111 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1765,6 +1765,7 @@ 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) ||
@@ -1773,7 +1774,14 @@ 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);
@@ -2537,8 +2545,6 @@ 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;
@@ -2635,6 +2641,7 @@ 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);
@@ -2648,6 +2655,7 @@ 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);
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 591dba6..b051f0d 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -402,6 +402,8 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
loff_t pos;
ssize_t ret;
+ sb_start_write(inode->i_sb);
+
mutex_lock(&inode->i_mutex);
if (!access_ok(VERIFY_READ, buf, len)) {
@@ -412,8 +414,6 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
pos = *ppos;
count = len;
- 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;
@@ -435,6 +435,7 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
current->backing_dev_info = NULL;
out_up:
mutex_unlock(&inode->i_mutex);
+ sb_end_write(inode->i_sb);
return ret;
}
EXPORT_SYMBOL_GPL(xip_file_write);
--
1.7.1
--
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