lkml.org 
[lkml]   [2009]   [Nov]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 2/2] drm: mm always protect change to unused_nodes with unused_lock spinlock
    From
    Date
    On Mon, 2009-11-16 at 17:23 +0100, Thomas Hellstrom wrote:
    > Dave Airlie wrote:
    > > On Sat, Nov 14, 2009 at 5:56 AM, Jerome Glisse <jglisse@redhat.com> wrote:
    > >
    > >> unused_nodes modification needs to be protected by unused_lock spinlock.
    > >> Here is an example of an usage where there is no such protection without
    > >> this patch.
    > >>
    > >> Process 1: 1-drm_mm_pre_get(this function modify unused_nodes list)
    > >> 2-spin_lock(spinlock protecting mm struct)
    > >> 3-drm_mm_put_block(this function might modify unused_nodes
    > >> list but doesn't protect modification with unused_lock)
    > >> 4-spin_unlock(spinlock protecting mm struct)
    > >> Process2: 1-drm_mm_pre_get(this function modify unused_nodes list)
    > >> At this point Process1 & Process2 might both be doing modification to
    > >> unused_nodes list. This patch add unused_lock protection into
    > >> drm_mm_put_block to avoid such issue.
    > >>
    > >
    > > Have we got a bug number or reproducer for this?
    > >
    > > I've cc'ed Thomas and Chris who were last ppl to touch drm_mm.c for some
    > > sort of acks.
    > >
    > > Dave.
    > >
    > >
    > >> Signed-off-by: Jerome Glisse <jglisse@redhat.com>
    > >> ---
    > >> drivers/gpu/drm/drm_mm.c | 9 +++++++++
    > >> 1 files changed, 9 insertions(+), 0 deletions(-)
    > >>
    > >> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
    > >> index c861d80..97dc5a4 100644
    > >> --- a/drivers/gpu/drm/drm_mm.c
    > >> +++ b/drivers/gpu/drm/drm_mm.c
    > >> @@ -103,6 +103,11 @@ static struct drm_mm_node *drm_mm_kmalloc(struct drm_mm *mm, int atomic)
    > >> return child;
    > >> }
    > >>
    > >> +/* drm_mm_pre_get() - pre allocate drm_mm_node structure
    > >> + * drm_mm: memory manager struct we are pre-allocating for
    > >> + *
    > >> + * Returns 0 on success or -ENOMEM if allocation fails.
    > >> + */
    > >> int drm_mm_pre_get(struct drm_mm *mm)
    > >> {
    > >> struct drm_mm_node *node;
    > >> @@ -253,12 +258,14 @@ void drm_mm_put_block(struct drm_mm_node *cur)
    > >> prev_node->size += next_node->size;
    > >> list_del(&next_node->ml_entry);
    > >> list_del(&next_node->fl_entry);
    > >> + spin_lock(&mm->unused_lock);
    > >> if (mm->num_unused < MM_UNUSED_TARGET) {
    > >> list_add(&next_node->fl_entry,
    > >> &mm->unused_nodes);
    > >> ++mm->num_unused;
    > >> } else
    > >> kfree(next_node);
    > >> + spin_unlock(&mm->unused_lock);
    > >> } else {
    > >> next_node->size += cur->size;
    > >> next_node->start = cur->start;
    > >> @@ -271,11 +278,13 @@ void drm_mm_put_block(struct drm_mm_node *cur)
    > >> list_add(&cur->fl_entry, &mm->fl_entry);
    > >> } else {
    > >> list_del(&cur->ml_entry);
    > >> + spin_lock(&mm->unused_lock);
    > >> if (mm->num_unused < MM_UNUSED_TARGET) {
    > >> list_add(&cur->fl_entry, &mm->unused_nodes);
    > >> ++mm->num_unused;
    > >> } else
    > >> kfree(cur);
    > >> + spin_unlock(&mm->unused_lock);
    > >> }
    > >> }
    > >>
    > >> --
    > >> 1.6.5.2
    > >>
    > >>
    > >>
    > Hmm. Ouch. The patch looks correct, although I'm not 100% sure it's OK
    > to kfree() within a spinlocked region? Perhaps better to take it out.

    Would kfree() possibly sleep? I wouldn't think so, if not it should be
    safe.

    robert.

    > /Thomas
    >
    >
    >
    >
    > ------------------------------------------------------------------------------
    > Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
    > trial. Simplify your report design, integration and deployment - and focus on
    > what you do best, core application coding. Discover what's new with
    > Crystal Reports now. http://p.sf.net/sfu/bobj-july
    > --
    > _______________________________________________
    > Dri-devel mailing list
    > Dri-devel@lists.sourceforge.net
    > https://lists.sourceforge.net/lists/listinfo/dri-devel
    --
    Robert Noland <rnoland@2hip.net>
    2Hip Networks



    \
     
     \ /
      Last update: 2009-11-16 18:05    [W:0.031 / U:30.116 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site