lkml.org 
[lkml]   [2016]   [Sep]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability
    On Thu, Sep 29, 2016 at 09:43:53AM -0700, Paul E. McKenney wrote:
    > If two processes are related by a RELEASE+ACQUIRE pair, ordering can be
    > broken if a third process overwrites the value written by the RELEASE
    > operation before the ACQUIRE operation has a chance of reading it, for
    > example:
    >
    > P0(int *x, int *y)
    > {
    > WRITE_ONCE(*x, 1);
    > smp_store_release(y, 1);
    > }
    >
    > P1(int *y)
    > {
    > smp_store_release(y, 2);
    > }
    >
    > P2(int *x, int *y)
    > {
    > r1 = smp_load_acquire(y);
    > r2 = READ_ONCE(*x);
    > }
    >
    > Both ARM and powerpc allow the "after the dust settles" outcome (r1=2 &&
    > r2=0), as does the current version of the early prototype Linux-kernel
    > memory model.
    >
    > This commit therefore updates the documentation to call this vulnerability
    > out explicitly.

    So its a pretty dumb thing to do in any case (and yes the kernel does
    this). Its also entirely expected in my book, that if you generate
    conflicting writes on a release, ordering is out the window.

    Why do we need to call this out? Who in his right mind would want to do
    this and expect anything other than wreckage?

    Not that we're not having too much 'fun' discussing this,.. but I do
    wonder why we need to call this out.

    \
     
     \ /
      Last update: 2016-09-30 12:25    [W:3.342 / U:0.108 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site