lkml.org 
[lkml]   [2017]   [Oct]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends()
    Date
    David Howells <dhowells@redhat.com> wrote:

    > Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
    >
    > > static inline void *assoc_array_ptr_to_leaf(const struct assoc_array_ptr *x)
    > > {
    > > - return (void *)((unsigned long)x & ~ASSOC_ARRAY_PTR_TYPE_MASK);
    > > + return (void *)((unsigned long)READ_ONCE(x) & /* Address dependency. */
    > > + ~ASSOC_ARRAY_PTR_TYPE_MASK);
    > > }
    >
    > This is the wrong place to do this. assoc_array_ptr_to_leaf() is effectively
    > no more than a special cast; it removes a metadata bit from a pointer. x is
    > the value we're modifying, not *x, and x was read by the caller.

    Also, x is not a pointer you can read from, so if READ_ONCE(x) ever effects a
    memory access, you might get an oops.

    David

    \
     
     \ /
      Last update: 2017-10-10 12:00    [W:6.729 / U:0.036 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site