Date:	Thu, 25 Apr 2013 16:09:24 +0800
From:	majianpeng <majianpeng@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
CC:	Andi Kleen <ak@...ux.intel.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [BUG] On x86_32 system, handle block-device which size is larger
 than 16TB.

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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