Re: [patch] truncate fixes

From: Andrew Morton (akpm@zip.com.au)
Date: Sun Jan 06 2002 - 22:48:38 EST


Andrea Arcangeli wrote:
>
> On Sat, Jan 05, 2002 at 03:08:25AM -0800, Andrew Morton wrote:
> > }
> > return 0;
> > out:
> > + bh = head;
> > + block_start = 0;
> > + do {
> > + if (buffer_new(bh) && !buffer_uptodate(bh)) {
> > + memset(kaddr+block_start, 0, bh->b_size);
> > + set_bit(BH_Uptodate, &bh->b_state);
> > + mark_buffer_dirty(bh);
> > + }
> > + block_start += bh->b_size;
> > + bh = bh->b_this_page;
> > + } while (bh != head);
> > return err;
> > }
>
> the above code will end marking uptodate (zeroed) buffers relative to
> blocks that cannot be read from disk. So a read-retry won't hit the disk
> and that's wrong.
>
> I think that will be fixed by additionally also return -EIO in the
> wait_on_buffer loop (instead of goto out), so we won't generate zeroed
> uptodate cache in case of read failure.
>

Right. There's also the case where get_block() returns -EIO when,
for example, it fails on reading an indirect block. We end up
writing zeroes into some of the blocks. But I think that behaviour
is correct.

(I think I'll add a buffer_mapped() test to this code as well. It's
a bit redundant because the fs shouldn't go setting BH_New and not
BH_Mapped, but this code is _very_ rarely executed, and I haven't
tested all filesystems...)

@@ -1633,12 +1660,22 @@ static int __block_prepare_write(struct
         */
        while(wait_bh > wait) {
                wait_on_buffer(*--wait_bh);
- err = -EIO;
                if (!buffer_uptodate(*wait_bh))
- goto out;
+ return -EIO;
        }
        return 0;
 out:
+ bh = head;
+ block_start = 0;
+ do {
+ if (buffer_new(bh) && buffer_mapped(bh) && !buffer_uptodate(bh)) {
+ memset(kaddr+block_start, 0, bh->b_size);
+ set_bit(BH_Uptodate, &bh->b_state);
+ mark_buffer_dirty(bh);
+ }
+ block_start += bh->b_size;
+ bh = bh->b_this_page;
+ } while (bh != head);
        return err;
 }
 
I'll retest this, including the -EIO path.
-
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