[PATCH 2/2] Handle error in sync_sb_inodes()

Guillaume Chazarain
2006-12-29T21:52:41Z

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Against 2.6.20-rc2, and now the bug fix.

--
Guillaume

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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 3859b1144d3a fs/fs-writeback.c
--- a/fs/fs-writeback.c Sun Dec 24 05:00:03 2006 +0000
+++ b/fs/fs-writeback.c Fri Dec 29 22:12:42 2006 +0100
@@ -316,6 +316,7 @@ 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);
@@ -365,7 +366,8 @@ 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);