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ext4: use pre-zeroed blocks for DAX page faults

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Make DAX fault path use pre-zeroed blocks to avoid races with extent
conversion and zeroing when two page faults to the same block happen.

Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2015-12-07 15:10:44 -05:00 committed by Theodore Ts'o
parent c86d8db33a
commit ba5843f51d
3 changed files with 74 additions and 36 deletions
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4
fs/ext4/ext4.h
View File

@ -2452,8 +2452,8 @@ struct buffer_head *ext4_getblk(handle_t *, struct inode *, ext4_lblk_t, int);
struct buffer_head *ext4_bread(handle_t *, struct inode *, ext4_lblk_t, int);
int ext4_get_block_write(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create);
int ext4_get_block_dax(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create);
int ext4_dax_mmap_get_block(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create);
int ext4_get_block(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create);
int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,

20
fs/ext4/file.c
View File

@ -193,18 +193,6 @@ out:
}
#ifdef CONFIG_FS_DAX
static void ext4_end_io_unwritten(struct buffer_head *bh, int uptodate)
{
struct inode *inode = bh->b_assoc_map->host;
/* XXX: breaks on 32-bit > 16TB. Is that even supported? */
loff_t offset = (loff_t)(uintptr_t)bh->b_private << inode->i_blkbits;
int err;
if (!uptodate)
return;
WARN_ON(!buffer_unwritten(bh));
err = ext4_convert_unwritten_extents(NULL, inode, offset, bh->b_size);
}
static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
int result;
@ -225,8 +213,7 @@ static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
if (IS_ERR(handle))
result = VM_FAULT_SIGBUS;
else
result = __dax_fault(vma, vmf, ext4_get_block_dax,
ext4_end_io_unwritten);
result = __dax_fault(vma, vmf, ext4_dax_mmap_get_block, NULL);
if (write) {
if (!IS_ERR(handle))
@ -262,7 +249,7 @@ static int ext4_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
result = VM_FAULT_SIGBUS;
else
result = __dax_pmd_fault(vma, addr, pmd, flags,
ext4_get_block_dax, ext4_end_io_unwritten);
ext4_dax_mmap_get_block, NULL);
if (write) {
if (!IS_ERR(handle))
@ -283,8 +270,7 @@ static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
sb_start_pagefault(inode->i_sb);
file_update_time(vma->vm_file);
down_read(&EXT4_I(inode)->i_mmap_sem);
err = __dax_mkwrite(vma, vmf, ext4_get_block_dax,
ext4_end_io_unwritten);
err = __dax_mkwrite(vma, vmf, ext4_dax_mmap_get_block, NULL);
up_read(&EXT4_I(inode)->i_mmap_sem);
sb_end_pagefault(inode->i_sb);

86
fs/ext4/inode.c
View File

@ -723,16 +723,6 @@ static int _ext4_get_block(struct inode *inode, sector_t iblock,
map_bh(bh, inode->i_sb, map.m_pblk);
bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
if (IS_DAX(inode) && buffer_unwritten(bh)) {
/*
* dgc: I suspect unwritten conversion on ext4+DAX is
* fundamentally broken here when there are concurrent
* read/write in progress on this inode.
*/
WARN_ON_ONCE(io_end);
bh->b_assoc_map = inode->i_mapping;
bh->b_private = (void *)(unsigned long)iblock;
}
if (io_end && io_end->flag & EXT4_IO_END_UNWRITTEN)
set_buffer_defer_completion(bh);
bh->b_size = inode->i_sb->s_blocksize * map.m_len;
@ -3097,17 +3087,79 @@ static int ext4_get_block_overwrite(struct inode *inode, sector_t iblock,
return ret;
}
int ext4_get_block_dax(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create)
#ifdef CONFIG_FS_DAX
int ext4_dax_mmap_get_block(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create)
{
int flags = EXT4_GET_BLOCKS_PRE_IO | EXT4_GET_BLOCKS_UNWRIT_EXT;
int ret, err;
int credits;
struct ext4_map_blocks map;
handle_t *handle = NULL;
int flags = 0;
if (create)
flags |= EXT4_GET_BLOCKS_CREATE;
ext4_debug("ext4_get_block_dax: inode %lu, create flag %d\n",
ext4_debug("ext4_dax_mmap_get_block: inode %lu, create flag %d\n",
inode->i_ino, create);
return _ext4_get_block(inode, iblock, bh_result, flags);
map.m_lblk = iblock;
map.m_len = bh_result->b_size >> inode->i_blkbits;
credits = ext4_chunk_trans_blocks(inode, map.m_len);
if (create) {
flags |= EXT4_GET_BLOCKS_PRE_IO | EXT4_GET_BLOCKS_CREATE_ZERO;
handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, credits);
if (IS_ERR(handle)) {
ret = PTR_ERR(handle);
return ret;
}
}
ret = ext4_map_blocks(handle, inode, &map, flags);
if (create) {
err = ext4_journal_stop(handle);
if (ret >= 0 && err < 0)
ret = err;
}
if (ret <= 0)
goto out;
if (map.m_flags & EXT4_MAP_UNWRITTEN) {
int err2;
/*
* We are protected by i_mmap_sem so we know block cannot go
* away from under us even though we dropped i_data_sem.
* Convert extent to written and write zeros there.
*
* Note: We may get here even when create == 0.
*/
handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, credits);
if (IS_ERR(handle)) {
ret = PTR_ERR(handle);
goto out;
}
err = ext4_map_blocks(handle, inode, &map,
EXT4_GET_BLOCKS_CONVERT | EXT4_GET_BLOCKS_CREATE_ZERO);
if (err < 0)
ret = err;
err2 = ext4_journal_stop(handle);
if (err2 < 0 && ret > 0)
ret = err2;
}
out:
WARN_ON_ONCE(ret == 0 && create);
if (ret > 0) {
map_bh(bh_result, inode->i_sb, map.m_pblk);
bh_result->b_state = (bh_result->b_state & ~EXT4_MAP_FLAGS) |
map.m_flags;
/*
* At least for now we have to clear BH_New so that DAX code
* doesn't attempt to zero blocks again in a racy way.
*/
bh_result->b_state &= ~(1 << BH_New);
bh_result->b_size = map.m_len << inode->i_blkbits;
ret = 0;
}
return ret;
}
#endif
static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
ssize_t size, void *private)