I/O errors could go unnoticed when syncing, for example the following code could
write a file bigger than 10Mib on a 10Mib filesystem. With this patch, msync()
will report the error originally encountered by sync(). Tuning the number of
sync may be needed to reproduce the bug.
make_file.c:

#include <unistd.h>
#include <sys/fcntl.h>
#include <sys/mman.h>
#include <string.h>
#include <stdio.h>

#define NR_SYNC 3 /* Adjust me if needed */
#define SIZE ((10 << 20) + (100 << 10))

int main(void)
{
	int i, fd;
	char *mapping;
	fd = open("mnt/file", O_RDWR | O_CREAT, 0600);
	if (fd < 0) {
		perror("open");
		return 1;
	}

	if (ftruncate(fd, SIZE) < 0) {
		perror("ftruncate");
		return 1;
	}

	mapping = mmap(NULL, SIZE, PROT_WRITE, MAP_SHARED, fd, 0);
	if (mapping == MAP_FAILED) {
		perror("mmap");
		return 1;
	}

	memset(mapping, 0xFF, SIZE);

	for (i = 0; i < NR_SYNC; i++)
		sync();

	if (msync(mapping, SIZE, MS_SYNC) < 0) {
		perror("msync");
		return 1;
	}

	if (close(fd) < 0) {
		perror("close");
		return 1;
	}

	puts("File written successfully => bad!\n");
	return 0;
}

#!/bin/sh

dd if=/dev/zero of=fs.10M bs=10M count=0 seek=1
mkfs.ext2 -qF fs.10M
mkdir mnt
mount fs.10M mnt -o loop
./make_file

Signed-off-by: Guillaume Chazarain <guichaz@yahoo.fr>
---

 fs-writeback.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff -r ecb3a0d111ec fs/fs-writeback.c
--- a/fs/fs-writeback.c	Fri Feb 09 15:31:50 2007 +0100
+++ b/fs/fs-writeback.c	Fri Feb 09 23:10:47 2007 +0100
@@ -327,6 +327,7 @@ sync_sb_inodes(struct super_block *sb, s
 		struct address_space *mapping = inode->i_mapping;
 		struct backing_dev_info *bdi = mapping->backing_dev_info;
 		long pages_skipped;
+		int ret;
 
 		if (!bdi_cap_writeback_dirty(bdi)) {
 			list_move(&inode->i_list, &sb->s_dirty);
@@ -376,7 +377,8 @@ sync_sb_inodes(struct super_block *sb, s
 		BUG_ON(inode->i_state & I_FREEING);
 		__iget(inode);
 		pages_skipped = wbc->pages_skipped;
-		__writeback_single_inode(inode, wbc);
+		ret = __writeback_single_inode(inode, wbc);
+		mapping_set_error(mapping, ret);
 		if (wbc->sync_mode == WB_SYNC_HOLD) {
 			inode->dirtied_when = jiffies;
 			list_move(&inode->i_list, &sb->s_dirty);