lkml.org 
[lkml]   [2008]   [Dec]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 01/15] kmemleak: Add the base support
    Hi Catalin,

    On Sat, Nov 29, 2008 at 12:43 PM, Catalin Marinas
    <catalin.marinas@arm.com> wrote:
    > +/*
    > + * Insert a pointer into the pointer hash table.
    > + */
    > +static inline void create_object(unsigned long ptr, size_t size, int ref_count)
    > +{

    [...]

    > + if (ptr < min_addr)
    > + min_addr = ptr;
    > + if (ptr + size > max_addr)
    > + max_addr = ptr + size;
    > + /*
    > + * Update the boundaries before inserting the object in the
    > + * prio search tree.
    > + */
    > + smp_mb();

    I'm not sure I understand the purpose of this memory barrier. As soon
    as some other CPU acquires object_tree_lock, updates to the boundaries
    will be visible due to the implicit memory barriers in locking
    functions (see Documentation/memory-barrier.txt for details).

    However, I'm wondering why this isn't a smp_wmb() and..

    > +/*
    > + * Scan a block of memory (exclusive range) for pointers and move
    > + * those found to the gray list.
    > + */
    > +static void scan_block(void *_start, void *_end, struct memleak_object *scanned)
    > +{
    > + unsigned long *ptr;
    > + unsigned long *start = PTR_ALIGN(_start, BYTES_PER_WORD);
    > + unsigned long *end = _end - (BYTES_PER_WORD - 1);
    > +
    > + for (ptr = start; ptr < end; ptr++) {

    ...why don't we have the pairing smp_rmb() here before we read
    min_addr and max_addr?

    > +
    > + /*
    > + * The boundaries check doesn't need to be precise
    > + * (hence no locking) since orphan objects need to
    > + * pass a scanning threshold before being reported.
    > + */
    > + if (pointer < min_addr || pointer >= max_addr)
    > + continue;

    Pekka


    \
     
     \ /
      Last update: 2008-12-01 08:17    [W:0.022 / U:62.376 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site