Well, my original post got ZERO responses, but I've continued to look
at this, and with the help of a colleague I think we've bottomed out.
do_generic_file_read does indeed have a bug, as mentioned below. However,
this bug is generally not hit as the call to a_ops->readpage (normally
pointing at blkdev_readpage) NEVER returns an error. However, the Veritas
code's readpage does return errors, and this triggers this KERNEL BUG.
I don't know enough about the page cache to know if simply NULLing the
page->mapping pointer is safe.
Anyone care to address this?
thanks
- jim
On Mon, 9 May 2005 08:02:05 -0700 (PDT)
Jim Washer <[email protected]> wrote:
>
> I've been looking at a stack trace from a 2.4.x kenrel where the kernel
> hits the "page has mapping still set" BUG() in __free_pages_ok.
>
> What I've found is that in do_generic_file_read, the call:
> error = mapping->a_ops->readpage(filp, page);
>
> is returning an error (EFAULT)
>
> However, shortly after, we fall into:
> /* UHHUH! A synchronous read error occurred. Report it */
> desc->error = error;
> page_cache_release(page);
> break;
>
> This code tries to free the page in question. However, is it reasonable for
> do_generic_file_read to free a page "that belongs to" filesystem code?
>
> Is there some (un)written rule that says filesystem readpage code MUST
> unmap a page before returning an error?
>
>
> I notice that several other locations in do_generic_file_read first check
> that the page has no mapping before freeing, but not here.
>
>
> Further details.
> 1)The file system in question is veritas VXFS, which is NOT open source.
> However, I'm asking this as a general question about whether or not
> there is a requirement that an given FS unmap a page before returning
> an error
>
> 2)The kernel is RHEL3u3, but the code path here apprears the same in 2.4.30
>
> 3)I've not included the stack trace here, as it came from a RHEL3 kernel,
> which I assume most reader of lkml would not have access to.
> I don't want to get into arguing about the analysis of this particular
> stack, but rather I want to consider if the attempted page free in
> do_generic_file_read is "correct" in ALL cases.
>
>
> thanks for considering this.
>
> - jim
>
>
> --
> James Washer
> IBM Linux Change Team
> -
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--
James Washer
IBM Linux Change Team
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