[PATCH review 0/7] Bind mount escape fixes

Eric W. Biederman ebiederm at xmission.com
Fri Aug 21 15:27:33 UTC 2015

On August 21, 2015 12:51:05 AM PDT, Al Viro <viro at ZenIV.linux.org.uk> wrote:
>On Sun, Aug 16, 2015 at 06:33:21AM -0500, Eric W. Biederman wrote:
>> > ... or either of us can do merging those checks into a single
>> > be it as a followup to your 7-patch series, or folded with the
>> > fs/dcache.c-affecting patches in there.  If you have no time left,
>I can
>> > certainly do that followup myself - not a problem[1]
>> I don't have time.  Everytime I have worked with this it has take
>> much full days of staring at the code, and I don't have any more full
>> days left before the merge window.
>OK, at that point I've pretty much given up on fs_pin for this cycle.
>And testing your variant with unconditional checks on .. appears to
>fairly low overhead.  I still want to deal with catching and unmounting
>unreachable suckers, so fs/dcache.c side of things will get used when
>we get
>to that stuff, but for now I've taken your 1/7, 2/7 plus the variant of
>"vfs: Test for and handle paths that are unreachable from their
>that doesn't care whether anything escaped or not.
>3--6 are held in a local branch for now; I *am* going to use them
>come next cycle.  And there's another pile of fun around that area,
>for the next cycle - kernel-initiated subtree removals on things like
>sysfs et.al.; handling of the locking in those is inconsistent and tied
>with the fun we have for d_move()/__d_unalias().  Sigh...

I am sorry to hear about a mess in sysfs. 

I am glad to hear that we do not appear to need MNT_DIR_ESCAPED to avoid performance regressions.  That should make back porters lives much easier.

As for the future I have a suspicion that we want to look at the rcu readable dynamically sized hash tables the networking guys cooked up.

Al thank you very much for performance testing the simple version.



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