Currently it is possible for some errors to be detected at write-back time but not reported to the program as shown by the following script using the included make_file.c.
---------8<---------8<---------8<---------8<---------8<---------8<--------- #!/bin/sh # We binary search the size of a file in 40M filesystem that can cause # the missed error. MIN=5000000 MAX=50000000 rm fs.40M dd if=/dev/zero of=fs.40M bs=40M count=0 seek=1 status=noxfer #mkfs.ext2 -F fs.40M mkfs.ext3 -F fs.40M #mkfs.jfs -q fs.40M #mkfs.reiserfs -fq fs.40M #mkfs.xfs fs.40M attempt() { SIZE=$1 RES=0 ./make_file valid_file $SIZE mount fs.40M /mnt -o loop if ! ./make_file /mnt/not_enough_space $SIZE; then # We could not create the file as the requested size # was clearly too big RES=1 fi umount /mnt if [ $RES -eq 0 ]; then mount fs.40M /mnt -o loop if cmp valid_file /mnt/not_enough_space; then # The file was too small, it fitted in the filesystem RES=-1 fi umount /mnt fi if [ $RES -eq 0 ]; then echo "Undetected ENOSPC with SIZE=$SIZE" exit fi return $RES } while [ $((MAX - MIN)) -gt 1 ]; do SIZE=$(((MIN + MAX) / 2)) attempt $SIZE RES=$? if [ $RES -eq 1 ]; then MAX=$SIZE else MIN=$SIZE fi done echo "Could not reproduce the problem" ---------8<---------8<---------8<---------8<---------8<---------8<--------- /* make_file.c */ #include <unistd.h> #include <sys/fcntl.h> #include <sys/mman.h> #include <string.h> #include <stdio.h> #include <stdlib.h> int main(int argc, char **argv) { int size, fd; char *mapping; if (argc != 3) { fprintf(stderr, "Usage: %s FILE SIZE\n", argv[0]); return 1; } size = atoi(argv[2]); fd = open(argv[1], O_RDWR | O_CREAT, 0600); if (fd < 0) { perror(argv[1]); 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); /* Force a write-back */ sync(); if (msync(mapping, size, MS_SYNC) < 0) { perror("msync"); return 1; } if (close(fd) < 0) { perror("close"); return 1; } printf("%s: successfully written %d bytes\n", argv[1], size); return 0; } ---------8<---------8<---------8<---------8<---------8<---------8<--------- make_file.c mmaps a hole, performs some writeback (memset + sync) and then expects to find some error code in msync(). The script mounts a 40M loopback filesystem and does a binary search to find the size of a file big enough to provoke a ENOSPC, but small enough to show the error not being detected at msync() time. The error window is large enough for such a size to be quickly found, but with this patch, no such file size can be found. All mmap capable filesystems I tested are affected (ext2, ext3, jfs, reiserfs, xfs). XFS is special in that it survives the test thanks to the page_mkwrite() work, i.e. it SIGBUS during memset. Anyway, this behavious solves ENOSPC but does nothing for EIO. The offending code is in fs/fs-writeback.c: sync_sb_inodes(...) () { ... __writeback_single_inode(inode, wbc); ... } __writeback_single_inode() gets the error from mapping->flags, clears it and returns it. But sync_sb_inodes() ignores this return value. In -mm there is sync_sb_inodes-propagate-errors.patch that propagates the error from __writeback_single_inode upwards in the call stack. IMHO, this propagation is useless because: - the error is combined from the errors in all the synced inodes, so it just tells that some inode in a specific fs got an error, - nobody in the call stack is interested in this error: certainly not pdflush, or 'void sync(2)'. Signed-off-by: Guillaume Chazarain <[EMAIL PROTECTED]> --- fs/fs-writeback.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 0fca820..88bb3c4 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -417,6 +417,7 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc) struct address_space *mapping = inode->i_mapping; struct backing_dev_info *bdi = mapping->backing_dev_info; long pages_skipped; + int err; if (!bdi_cap_writeback_dirty(bdi)) { redirty_tail(inode); @@ -461,7 +462,8 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc) BUG_ON(inode->i_state & I_FREEING); __iget(inode); pages_skipped = wbc->pages_skipped; - __writeback_single_inode(inode, wbc); + err = __writeback_single_inode(inode, wbc); + mapping_set_error(mapping, err); if (wbc->sync_mode == WB_SYNC_HOLD) { inode->dirtied_when = jiffies; list_move(&inode->i_list, &sb->s_dirty); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/