Hi all,
Some time ago, I mentioned there are some problems on x86-32 system about handling md-block-device which size is larger than 16TB.
And i send a patch.But there are no concern with it.
The website of is: http://www.spinics.net/lists/linux-fsdevel/msg55672.html.
Except the wrapping problem, recently i found another problem.It will cause infinite loop.At lease i watched one hour, the programs don't end.
On x86-32 system, the version of kernel is 3.9-rc8. Disk is raid0 which size is about 17TB.
The test program is:
int main()
{
long long max_size = (4096LL << 32);
int fd = open("/dev/md0", O_RDWR);
off64_t off;
int ret;
char *buff = memalign(512, 4096);
if (buff == NULL) {
printf("memalign error %s\n", strerror(errno));
exit(-1);
}
if (fd < 0) {
printf("open error %s\n", strerror(errno));
return -errno;
}
if ((off = lseek64(fd, max_size - 2000, SEEK_SET)) < 0)
printf("lseek64 error %s\n", strerror(errno));
else
printf("off 0x%llx\n", off);
if ((ret = write(fd, buff, 4096)) < 0)
printf("write error %s\n", strerror(errno));
else
printf("write return %d\n", ret);
close(fd);
return 0;
}
If run this problem, it will not be end up.Because the close(fd) operation.
The reason is:
close(fd)---->blkdev_close-->sync_blockdev--->filemap_write_and_wait--->__filemap_fdatawrite_range--->do_writepages-->write_cache_pages.
In function write_cache_pages:
> nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
> min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
> if (nr_pages == 0)
> break;
Because there is only on dirty page which index is 0xFFFFFFFF.
> for (i = 0; i < nr_pages; i++) {
..........
> ret = (*writepage)(page, wbc, data);
So the function blkdev_writepage will be called.
blkdev_writepage---->block_write_full_page---->block_write_full_page_endio.
In function block_write_full_page_endio:
> struct inode * const inode = page->mapping->host;
> loff_t i_size = i_size_read(inode);
> const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
> unsigned offset;
> /* Is the page fully inside i_size? */
> if (page->index < end_index)
return __block_write_full_page(inode, page, get_block, wbc,
handler);
Because page->index is 0xfffffff,but the end_index is very litter because the wrapping.
On x86-32os, pgoff_t is unsigned long .So 17TB >> PAGE_CACHE_SHIFT will be overflow.
> /* Is the page fully outside i_size? (truncate in progress) */
> offset = i_size & (PAGE_CACHE_SIZE-1);
> if (page->index >= end_index+1 || !offset) {
Because end_index is less than page->index.So it will be return there.So the PAGECACHE_TAG_TOWRITE will not be clear.
So it will continue to do.
> /*
> * The page may have dirty, unmapped buffers. For example,
> * they may have been added in ext3_writepage(). Make them
> * freeable here, so the page does not leak.
> */
> do_invalidatepage(page, 0);
> unlock_page(page);
> return 0; /* don't care */
> }
The infinite loop will cause hung-task because the mutex_lock don't release.
My previous patch is try to resolve this problem by add some judgement on lseek/read/write operation on block-device.
I think there are some place to deal with.
So i think we can using LFS rule on this.
The following is my new patch which adding LFS rule on block device.Because at present MAX_LFS_FILESIZE is equal 8GB -1.
But at present the pgoff_t is the type of unsigned long.So i update the definition of MAX_LFS_FILESIZE.
diff --git a/fs/block_dev.c b/fs/block_dev.c
index aae187a..f5ecd64 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -960,6 +960,8 @@ void check_disk_size_change(struct gendisk *disk, struct block_device *bdev)
disk_size = (loff_t)get_capacity(disk) << 9;
bdev_size = i_size_read(bdev->bd_inode);
+ if (bdev_size > bdev->bd_inode->i_sb->s_maxbytes)
+ bdev_size = bdev->bd_inode->i_sb->s_maxbytes;
if (disk_size != bdev_size) {
char name[BDEVNAME_SIZE];
@@ -1034,6 +1036,8 @@ void bd_set_size(struct block_device *bdev, loff_t size)
{
unsigned bsize = bdev_logical_block_size(bdev);
+ if (size > bdev->bd_inode->i_sb->s_maxbytes)
+ size = bdev->bd_inode->i_sb->s_maxbytes;
mutex_lock(&bdev->bd_inode->i_mutex);
i_size_write(bdev->bd_inode, size);
mutex_unlock(&bdev->bd_inode->i_mutex);
diff --git a/fs/libfs.c b/fs/libfs.c
index 916da8c..62aab9f 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -13,6 +13,7 @@
#include <linux/exportfs.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h> /* sync_mapping_buffers */
+#include <linux/magic.h>
#include <asm/uaccess.h>
@@ -230,8 +231,10 @@ struct dentry *mount_pseudo(struct file_system_type *fs_type, char *name,
s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL);
if (IS_ERR(s))
return ERR_CAST(s);
-
- s->s_maxbytes = MAX_LFS_FILESIZE;
+ if (magic == BDEVFS_MAGIC)
+ s->s_maxbytes = ((MAX_LFS_FILESIZE >> 9) << 9);
+ else
+ s->s_maxbytes = MAX_LFS_FILESIZE;
s->s_blocksize = PAGE_SIZE;
s->s_blocksize_bits = PAGE_SHIFT;
s->s_magic = magic;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2c28271..2888c4e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -869,7 +869,7 @@ static inline int file_check_writeable(struct file *filp)
/* Page cache limit. The filesystems should put that into their s_maxbytes
limits, otherwise bad things can happen in VM. */
#if BITS_PER_LONG==32
-#define MAX_LFS_FILESIZE (((loff_t)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1)
+#define MAX_LFS_FILESIZE (((loff_t)PAGE_CACHE_SIZE << (BITS_PER_LONG))-1)
#elif BITS_PER_LONG==64
#define MAX_LFS_FILESIZE ((loff_t)0x7fffffffffffffffLL)
#endif
Thanks
Jianpeng Ma
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