Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem

From	Al Viro <viro@ZenIV.linux.org.uk>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem
Date	2016-01-15 01:10 +0100
Message-ID	<qR07M-6ou-7@gated-at.bofh.it> (permalink)
References	(5 earlier) <qQVB8-34k-13@gated-at.bofh.it> <qQXjA-4eb-13@gated-at.bofh.it> <qQXWi-4xw-37@gated-at.bofh.it> <qQYz0-5b5-21@gated-at.bofh.it> <qQZY5-63s-1@gated-at.bofh.it>
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On Thu, Jan 14, 2016 at 03:58:22PM -0800, Linus Torvalds wrote:
> On Thu, Jan 14, 2016 at 2:25 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > For one thing, we'll lose RCU ->get_link() for those.
> 
> Why couldn't we just do that in the RCU walker? kmap should be fine..

In map_new_virtual():
                        __set_current_state(TASK_UNINTERRUPTIBLE);
                        add_wait_queue(pkmap_map_wait, &wait);
                        unlock_kmap();
                        schedule();
                        remove_wait_queue(pkmap_map_wait, &wait);
                        lock_kmap();
IOW, not in RCU mode ;-/

> That said, as long as you think it's ok now, I guess I don't care.
> Having some sanity testing in __add_to_page_cache_locked might be a
> good safety net.

That's better as a separate commit, IMO.  The thing I'm not sure about is
whether we want a BUG() in there - VM_WARN_ON(), perhaps?  OTOH, we do
have VM_BUG_ON_PAGE() in the same place already...

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Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into  highmem Al Viro <viro@ZenIV.linux.org.uk> - 2016-01-14 16:40 +0100
  Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem Tomeu Vizoso <tomeu@tomeuvizoso.net> - 2016-01-14 17:00 +0100
    Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into  highmem Al Viro <viro@ZenIV.linux.org.uk> - 2016-01-14 17:30 +0100
      Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem Tomeu Vizoso <tomeu@tomeuvizoso.net> - 2016-01-14 18:00 +0100
        Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into  highmem Al Viro <viro@ZenIV.linux.org.uk> - 2016-01-14 18:20 +0100
          Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem Tomeu Vizoso <tomeu@tomeuvizoso.net> - 2016-01-14 20:20 +0100
            Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into  highmem Al Viro <viro@ZenIV.linux.org.uk> - 2016-01-14 22:10 +0100
              Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem Linus Torvalds <torvalds@linux-foundation.org> - 2016-01-14 22:50 +0100
                Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into  highmem Al Viro <viro@ZenIV.linux.org.uk> - 2016-01-14 23:30 +0100
                Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into  highmem Al Viro <viro@ZenIV.linux.org.uk> - 2016-01-15 00:40 +0100
                Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem Linus Torvalds <torvalds@linux-foundation.org> - 2016-01-15 01:00 +0100
                Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into  highmem Al Viro <viro@ZenIV.linux.org.uk> - 2016-01-15 01:10 +0100

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