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Btrfs: Clean pte corresponding to page straddling i_size

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When extending a file by either "truncate up" or by writing beyond i_size, the
page which had i_size needs to be marked "read only" so that future writes to
the page via mmap interface causes btrfs_page_mkwrite() to be invoked. If not,
a write performed after extending the file via the mmap interface will find
the page to be writaeable and continue writing to the page without invoking
btrfs_page_mkwrite() i.e. we end up writing to a file without reserving disk
space.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Chandan Rajendra 2016-01-21 15:56:03 +05:30 committed by David Sterba
parent 5a2834f808
commit 27772b68f6
2 changed files with 11 additions and 3 deletions
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12
fs/btrfs/file.c
View file

@ -1778,6 +1778,8 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
ssize_t err;
loff_t pos;
size_t count;
loff_t oldsize;
int clean_page = 0;
mutex_lock(&inode->i_mutex);
err = generic_write_checks(iocb, from);
@ -1816,14 +1818,17 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
pos = iocb->ki_pos;
count = iov_iter_count(from);
start_pos = round_down(pos, root->sectorsize);
if (start_pos > i_size_read(inode)) {
oldsize = i_size_read(inode);
if (start_pos > oldsize) {
/* Expand hole size to cover write data, preventing empty gap */
end_pos = round_up(pos + count, root->sectorsize);
err = btrfs_cont_expand(inode, i_size_read(inode), end_pos);
err = btrfs_cont_expand(inode, oldsize, end_pos);
if (err) {
mutex_unlock(&inode->i_mutex);
goto out;
}
if (start_pos > round_up(oldsize, root->sectorsize))
clean_page = 1;
}
if (sync)
@ -1835,6 +1840,9 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
num_written = __btrfs_buffered_write(file, from, pos);
if (num_written > 0)
iocb->ki_pos = pos + num_written;
if (clean_page)
pagecache_isize_extended(inode, oldsize,
i_size_read(inode));
}
mutex_unlock(&inode->i_mutex);

2
fs/btrfs/inode.c
View file

@ -4899,7 +4899,6 @@ static int btrfs_setsize(struct inode *inode, struct iattr *attr)
}
if (newsize > oldsize) {
truncate_pagecache(inode, newsize);
/*
* Don't do an expanding truncate while snapshoting is ongoing.
* This is to ensure the snapshot captures a fully consistent
@ -4922,6 +4921,7 @@ static int btrfs_setsize(struct inode *inode, struct iattr *attr)
i_size_write(inode, newsize);
btrfs_ordered_update_i_size(inode, i_size_read(inode), NULL);
pagecache_isize_extended(inode, oldsize, newsize);
ret = btrfs_update_inode(trans, root, inode);
btrfs_end_write_no_snapshoting(root);
btrfs_end_transaction(trans, root);