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SubjectRe: [PATCH] 2.3.1[34]: filemap_nopage faults on ->readpage() failure
On Thu, Aug 19, 1999 at 12:35:22PM -0400, Chuck Lever wrote:

> good spotting... i looked at this a while back with the same suspicion.
> locking the page again, as in your patch, will cause a deadlock.

Ah yes, if readpage() leaves the page locked? I wasn't sure what other
implementations did (block_read_full_page doesn't ever fail), and I was too
lazy to check ;-)

> i think the readpage implementations are careful enough to leave the page
> locked if they return an error, but it might be good to review each.

nfs/read.c:nfs_readpage() doesn't seem to. Do we fix it, or try to handle this
in filemap_nopage? Ack, smb_readpage is weird, too -- it seems to expect the
page /not/ to be locked. Am I right in thinking that smbfs hasn't been
sanitised since the "Great Overhaul"?

> if (!error) {
> wait_on_page(page);
> if (Page_Uptodate(page))
> goto success;
> lock_page(page);
> ^^^^^^^^^^^^^^^^
> }

Okay, that makes sense. New patch (untested, but 'obviously' correct.. again):

--- filemap.c.orig Thu Aug 19 08:37:26 1999
+++ filemap.c Thu Aug 19 22:41:39 1999
@@ -1378,6 +1378,7 @@
if (Page_Uptodate(page))
goto success;
+ lock_page(page);

@@ -1386,8 +1387,11 @@
* because there really aren't any performance issues here
* and we need to check for errors.
- if (!PageLocked(page))
- PAGE_BUG(page);
+ if (Page_Uptodate(page)) {
+ UnlockPage(page);
+ goto success;
+ }
error = inode->i_op->readpage(file, page);
if (error)
> do you have a test case?

Yup, I have a Cheapbytes Debian 2.1R2 CD with a few suitably buggered files.
grep'ing them triggers the above problem quite nicely.

If smoking is so bad for you, how come it cures kippers?

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