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Subject[PATCH] one-liner fix for bforget() honoring BH_Protected; was: Re: Patch (repost): cramfs memory corruption fix
Linus Torvalds wrote:
>
> On Sat, 6 Jan 2001, Adam J. Richter wrote:
> >
> > This sounds like a bug that I posted a fix for a long time ago.
> > cramfs calls bforget on the superblock area, destroying that block of
> > the ramdisk, even when the ramdisk does not contain a cramfs file system.
> > Normally, bforget is called on block that really can be trashed,
> > such as blocks release by truncate or unlink.
>
> I'd really prefer just not letting bforget() touch BH_Protected buffers.
> bforget() is also used by other things than unlink/truncate: it's used by
> various partition codes etc, and it's used by the raid logic.

Yup, I backed out Adam's one-liner in favor of the attached one-liner.
Tested on 2.4.0, but should patch cleanly to just about anything. ;-)

BTW Linus - you were of course right on the cramfs wanting 4096
blocksize... but without this fix, that doesn't matter much. ;-)

regards,
David

--
David L. Parsley
Network Administrator
Roanoke College--- linux.linus/fs/buffer.c Wed Jan 3 23:45:26 2001
+++ linux/fs/buffer.c Wed Jan 10 15:49:36 2001
@@ -1145,13 +1145,15 @@
* free list if it can.. We can NOT free the buffer if:
* - there are other users of it
* - it is locked and thus can have active IO
+ * - it is marked BH_Protected
*/
void __bforget(struct buffer_head * buf)
{
/* grab the lru lock here to block bdflush. */
spin_lock(&lru_list_lock);
write_lock(&hash_table_lock);
- if (!atomic_dec_and_test(&buf->b_count) || buffer_locked(buf))
+ if (!atomic_dec_and_test(&buf->b_count) || buffer_locked(buf) ||
+ buffer_protected(buf))
goto in_use;
__hash_unlink(buf);
remove_inode_queue(buf);
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