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RDMA/umem: Get rid of per_mm->notifier_count

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This is intrinsically racy and the scheme is simply unnecessary. New MR
registration can wait for any on going invalidation to fully complete.

      CPU0                              CPU1
                                  if (atomic_read())
 if (atomic_dec_and_test() &&
     !list_empty())
  { /* not taken */ }
                                       list_add()

Putting the new UMEM into some kind of purgatory until another invalidate
rolls through..

Instead hold the read side of the umem_rwsem across the pair'd start/end
and get rid of the racy 'deferred add' approach.

Since all umem's in the rbt are always ready to go, also get rid of the
mn_counters_active stuff.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
This commit is contained in:
Jason Gunthorpe
2018-09-16 20:48:09 +03:00
committed by Doug Ledford
parent f27a0d50a4
commit ca748c39ea
2 changed files with 18 additions and 110 deletions
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15
include/rdma/ib_umem_odp.h
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@@ -67,15 +67,9 @@ struct ib_umem_odp {
struct mutex umem_mutex;
void *private; /* for the HW driver to use. */
/* When false, use the notifier counter in the ucontext struct. */
bool mn_counters_active;
int notifiers_seq;
int notifiers_count;
/* A linked list of umems that don't have private mmu notifier
* counters yet. */
struct list_head no_private_counters;
/* Tree tracking */
struct umem_odp_node interval_tree;
@@ -99,11 +93,8 @@ struct ib_ucontext_per_mm {
struct rb_root_cached umem_tree;
/* Protects umem_tree */
struct rw_semaphore umem_rwsem;
atomic_t notifier_count;
struct mmu_notifier mn;
/* A list of umems that don't have private mmu notifier counters yet. */
struct list_head no_private_counters;
unsigned int odp_mrs_count;
struct list_head ucontext_list;
@@ -162,12 +153,6 @@ static inline int ib_umem_mmu_notifier_retry(struct ib_umem_odp *umem_odp,
* and the ucontext umem_mutex semaphore locked for read).
*/
/* Do not allow page faults while the new ib_umem hasn't seen a state
* with zero notifiers yet, and doesn't have its own valid set of
* private counters. */
if (!umem_odp->mn_counters_active)
return 1;
if (unlikely(umem_odp->notifiers_count))
return 1;
if (umem_odp->notifiers_seq != mmu_seq)