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SubjectRe: ramdisk corruption problems - was: RE: pivot_root and initrdkern el panic woes
Alexander Viro wrote:
>
> Erm... I don't think so. Come on - vmtruncate() is obvious candidate
> for out-of-line. Please, look how it was done in 2.4.9-ac*.

Yeah, I thought that was just too damn ugly to make it out of my
ethernet port. Oh well, let's try it anyway.

> BTW, fs/buffer.c part of patch looks mangled.

Looks OK to me.

Here's the latest. It includes the block_write_full_page()
chunk (minus the access-bh-after-submit_bh bug which was in
the original).

So we have three chunks:

generic_file_write(): truncate the blocks when prepare_write()
fails. This is for ENOSPC on write-to-end-of-file.

block_write_full_page(): submit the blocks which we managed
to map. To prevent exposure of old data.

__block_prepare_write(): zero out and dirty the blocks which
we managed to instantiate. This is to prevent exposure of
stale data on ENOSPC during write() to mid-file.


Question: is the block_write_full_page() change correct? We
mark the page not-up-to-date, but end_buffer_io_async() is
going to mark it uptodate anyway.


And what should we do with BH_New?


--- linux-2.4.18-pre1/fs/buffer.c Fri Dec 21 11:19:14 2001
+++ linux-akpm/fs/buffer.c Sat Dec 29 23:39:11 2001
@@ -1512,6 +1512,7 @@ static int __block_write_full_page(struc
int err, i;
unsigned long block;
struct buffer_head *bh, *head;
+ int need_unlock;

if (!PageLocked(page))
BUG();
@@ -1567,8 +1568,34 @@ static int __block_write_full_page(struc
return 0;

out:
+ /*
+ * ENOSPC, or some other error. We may already have added some
+ * blocks to the file, so we need to write these out to avoid
+ * exposing stale data.
+ */
ClearPageUptodate(page);
- UnlockPage(page);
+ bh = head;
+ need_unlock = 1;
+ /* Recovery: lock and submit the mapped buffers */
+ do {
+ if (buffer_mapped(bh)) {
+ lock_buffer(bh);
+ need_unlock = 0;
+ }
+ bh = bh->b_this_page;
+ } while (bh != head);
+ do {
+ struct buffer_head *next = bh->b_this_page;
+ if (buffer_mapped(bh)) {
+ set_buffer_async_io(bh);
+ set_bit(BH_Uptodate, &bh->b_state);
+ clear_bit(BH_Dirty, &bh->b_state);
+ submit_bh(WRITE, bh);
+ }
+ bh = next;
+ } while (bh != head);
+ if (need_unlock)
+ UnlockPage(page);
return err;
}

@@ -1639,6 +1666,17 @@ static int __block_prepare_write(struct
}
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;
}

--- linux-2.4.18-pre1/mm/filemap.c Wed Dec 26 11:47:41 2001
+++ linux-akpm/mm/filemap.c Sat Dec 29 23:44:03 2001
@@ -3004,7 +3004,7 @@ generic_file_write(struct file *file,con
kaddr = kmap(page);
status = mapping->a_ops->prepare_write(file, page, offset, offset+bytes);
if (status)
- goto unlock;
+ goto sync_failure;
page_fault = __copy_from_user(kaddr+offset, buf, bytes);
flush_dcache_page(page);
status = mapping->a_ops->commit_write(file, page, offset, offset+bytes);
@@ -3029,6 +3029,7 @@ unlock:
if (status < 0)
break;
} while (count);
+done:
*ppos = pos;

if (cached_page)
@@ -3050,6 +3051,18 @@ out:
fail_write:
status = -EFAULT;
goto unlock;
+
+sync_failure:
+ /*
+ * If blocksize < pagesize, prepare_write() may have instantiated a
+ * few blocks outside i_size. Trim these off again.
+ */
+ kunmap(page);
+ UnlockPage(page);
+ page_cache_release(page);
+ if (pos + bytes > inode->i_size)
+ vmtruncate(inode, inode->i_size);
+ goto done;

o_direct:
written = generic_file_direct_IO(WRITE, file, (char *) buf, count, pos);
-
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