Commit 9ea7df53 authored by Jan Kara's avatar Jan Kara Committed by Al Viro

ext4: Rewrite ext4_page_mkwrite() to use generic helpers

Rewrite ext4_page_mkwrite() to use __block_page_mkwrite() helper. This
removes the need of using i_alloc_sem to avoid races with truncate which
seems to be the wrong locking order according to lock ordering documented in
mm/rmap.c. Also calling ext4_da_write_begin() as used by the old code seems to
be problematic because we can decide to flush delay-allocated blocks which
will acquire s_umount semaphore - again creating unpleasant lock dependency
if not directly a deadlock.

Also add a check for frozen filesystem so that we don't busyloop in page fault
when the filesystem is frozen.
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 58268691
......@@ -5843,80 +5843,84 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
struct page *page = vmf->page;
loff_t size;
unsigned long len;
int ret = -EINVAL;
void *fsdata;
int ret;
struct file *file = vma->vm_file;
struct inode *inode = file->f_path.dentry->d_inode;
struct address_space *mapping = inode->i_mapping;
handle_t *handle;
get_block_t *get_block;
int retries = 0;
/*
* Get i_alloc_sem to stop truncates messing with the inode. We cannot
* get i_mutex because we are already holding mmap_sem.
* This check is racy but catches the common case. We rely on
* __block_page_mkwrite() to do a reliable check.
*/
down_read(&inode->i_alloc_sem);
size = i_size_read(inode);
if (page->mapping != mapping || size <= page_offset(page)
|| !PageUptodate(page)) {
/* page got truncated from under us? */
goto out_unlock;
vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
/* Delalloc case is easy... */
if (test_opt(inode->i_sb, DELALLOC) &&
!ext4_should_journal_data(inode) &&
!ext4_nonda_switch(inode->i_sb)) {
do {
ret = __block_page_mkwrite(vma, vmf,
ext4_da_get_block_prep);
} while (ret == -ENOSPC &&
ext4_should_retry_alloc(inode->i_sb, &retries));
goto out_ret;
}
ret = 0;
lock_page(page);
wait_on_page_writeback(page);
if (PageMappedToDisk(page)) {
up_read(&inode->i_alloc_sem);
return VM_FAULT_LOCKED;
size = i_size_read(inode);
/* Page got truncated from under us? */
if (page->mapping != mapping || page_offset(page) > size) {
unlock_page(page);
ret = VM_FAULT_NOPAGE;
goto out;
}
if (page->index == size >> PAGE_CACHE_SHIFT)
len = size & ~PAGE_CACHE_MASK;
else
len = PAGE_CACHE_SIZE;
/*
* return if we have all the buffers mapped. This avoid
* the need to call write_begin/write_end which does a
* journal_start/journal_stop which can block and take
* long time
* Return if we have all the buffers mapped. This avoids the need to do
* journal_start/journal_stop which can block and take a long time
*/
if (page_has_buffers(page)) {
if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
ext4_bh_unmapped)) {
up_read(&inode->i_alloc_sem);
return VM_FAULT_LOCKED;
/* Wait so that we don't change page under IO */
wait_on_page_writeback(page);
ret = VM_FAULT_LOCKED;
goto out;
}
}
unlock_page(page);
/*
* OK, we need to fill the hole... Do write_begin write_end
* to do block allocation/reservation.We are not holding
* inode.i__mutex here. That allow * parallel write_begin,
* write_end call. lock_page prevent this from happening
* on the same page though
*/
ret = mapping->a_ops->write_begin(file, mapping, page_offset(page),
len, AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
if (ret < 0)
goto out_unlock;
ret = mapping->a_ops->write_end(file, mapping, page_offset(page),
len, len, page, fsdata);
if (ret < 0)
goto out_unlock;
ret = 0;
/*
* write_begin/end might have created a dirty page and someone
* could wander in and start the IO. Make sure that hasn't
* happened.
*/
lock_page(page);
wait_on_page_writeback(page);
up_read(&inode->i_alloc_sem);
return VM_FAULT_LOCKED;
out_unlock:
if (ret)
/* OK, we need to fill the hole... */
if (ext4_should_dioread_nolock(inode))
get_block = ext4_get_block_write;
else
get_block = ext4_get_block;
retry_alloc:
handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
if (IS_ERR(handle)) {
ret = VM_FAULT_SIGBUS;
up_read(&inode->i_alloc_sem);
goto out;
}
ret = __block_page_mkwrite(vma, vmf, get_block);
if (!ret && ext4_should_journal_data(inode)) {
if (walk_page_buffers(handle, page_buffers(page), 0,
PAGE_CACHE_SIZE, NULL, do_journal_get_write_access)) {
unlock_page(page);
ret = VM_FAULT_SIGBUS;
goto out;
}
ext4_set_inode_state(inode, EXT4_STATE_JDATA);
}
ext4_journal_stop(handle);
if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
goto retry_alloc;
out_ret:
ret = block_page_mkwrite_return(ret);
out:
return ret;
}
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