lkml.org 
[lkml]   [2007]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland
On 10/7/07, Pekka J Enberg <penberg@cs.helsinki.fi> wrote:
> On 10/7/07, Erez Zadok <ezk@cs.sunysb.edu> wrote:
> > Anyway, some Ubuntu users of Unionfs reported that msync(2) sometimes
> > returns AOP_WRITEPAGE_ACTIVATE (decimal 524288) back to userland.
> > Therefore, some user programs fail, esp. if they're written such as
> > this:
>
...
> It's a kernel bug. AOP_WRITEPAGE_ACTIVATE is a hint to the VM to avoid
> writeback of the page in the near future. I wonder if it's enough that we
> change the return value to zero from
> mm/page-writeback.c:write_cache_pages() in case we hit AOP_WRITEPAGE_ACTIVE...

Doesn't appear to be enough. I can't figure out why (since it appears
write_cache_pages bubbles up directly to sys_msync), but with that
patch applied, in my test case[1], msync returns -1 EIO. However,
with the exact same kernel without that patch applied, msync returns
524288 (AOP_WRITEPAGE_ACTIVATE). But as your patch specifically flips
524288 to 0, I can't figure out how it eventually returns -1 EIO.

Ryan

[1] "apt-get check" on a unionfs2 mount backed by tmpfs over cdrom,
standard livecd setup
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-10-08 04:01    [W:4.659 / U:0.804 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site